cwt 2.8.0

A Python implementation of CWT/COSE.

Python CWT - A Python implementation of CWT/COSE

Python CWT is a CBOR Web Token (CWT) and CBOR Object Signing and Encryption (COSE) implementation compliant with:

• RFC9052: CBOR Object Signing and Encryption (COSE): Structures and Process
• RFC9053: CBOR Object Signing and Encryption (COSE): Initial Algorithms
• RFC9338: CBOR Object Signing and Encryption (COSE): Countersignatures - experimental
• RFC8392: CWT (CBOR Web Token)
• draft-07: Use of HPKE with COSE - experimental
• draft-06: CWT Claims in COSE Headers - experimental
• and related various specifications. See Referenced Specifications.

It is designed to make users who already know about JWS/JWE/JWT be able to use it in ease. Little knowledge of CBOR/COSE/CWT is required to use it.

You can install Python CWT with pip:

$ pip install cwt

And then, you can use it as follows:

COSE API

from cwt import COSE, COSEKey

mac_key = COSEKey.generate_symmetric_key(alg="HS256", kid="01")

# The sender side:
sender = COSE.new()
encoded = sender.encode(
    b"Hello world!",
    mac_key,
    protected={"alg": "HS256"},
    unprotected={"kid": "01"},
)

# The recipient side:
recipient = COSE.new()
assert b"Hello world!" == recipient.decode(encoded, mac_key)

## You can get decoded protected/unprotected headers with the payload as follows:
# protected, unprotected, payload = recipient.decode_with_headers(encoded, mac_key)
# assert b"Hello world!" == payload

CWT API

import cwt
from cwt import COSEKey, CWTClaims

mac_key = COSEKey.generate_symmetric_key(alg="HS256", kid="01")

# The sender side:
token = encode(
    {
        CWTClaims.ISS: "coaps://as.example",
        CWTClaims.SUB: "dajiaji",
        CWTClaims.CTI: b"123",
    },
    mac_key,
)

# The recipient side:
decoded = decode(token, mac_key)
# decoded == {
#     CWTClaims.ISS: 'coaps://as.example',
#     CWTClaims.SUB: 'dajiaji',
#     CWTClaims.CTI: b'123',
#     CWTClaims.EXP: 1620088759,
#     CWTClaims.NBF: 1620085159,
#     CWTClaims.IAT: 1620085159
# }

Various usage examples are shown in this README.

See Documentation for details of the APIs.

Index

• Installation
• COSE Usage Examples
  • COSE MAC0
    • MAC with HMAC with SHA256
    • Countersign (MAC0)
  • COSE MAC
    • Direct Key Distribution
    • Direct Key with KDF
    • AES Key Wrap
    • Direct key Agreement
    • Key Agreement with Key Wrap
    • Countersign (MAC)
    • COSE-HPKE (MAC)
  • COSE Encrypt0
    • Encryption with ChaCha20/Poly1305
    • Countersign (Encrypt0)
    • COSE-HPKE (Encrypt0)
  • COSE Encrypt
    • Direct Key Distribution
    • Direct Key with KDF
    • AES Key Wrap
    • Direct key Agreement
    • Key Agreement with Key Wrap
    • Countersign (Encrypt)
    • COSE-HPKE (Encrypt)
  • COSE Signature1
    • Sign1 with EC P-256
    • Countersign (Sign1)
  • COSE Signature
    • Sign with EC P-256
    • Countersign (Sign)
• CWT Usage Examples
  • MACed CWT
  • Signed CWT
  • Encrypted CWT
  • Nested CWT
  • CWT with User Settings (e.g., expires_in)
  • CWT with User-Defined Claims
  • CWT with CWT claims in COSE headers
  • CWT with PoP Key
  • CWT with Private CA
  • CWT for EUDCC (EU Digital COVID Certificate)
• API Reference
• Supported CWT Claims
• Supported COSE Algorithms
• Referenced Specifications
• Tests
• Contributing

Installation

Install with pip:

pip install cwt

COSE Usage Examples

Followings are typical and basic examples which encode various types of COSE messages and decode them.

See API Reference.

COSE MAC0

MAC with HMAC with SHA256

Create a COSE MAC0 message, verify and decode it as follows:

from cwt import COSE, COSEKey

mac_key = COSEKey.generate_symmetric_key(alg="HS256", kid="01")

# The sender side:
sender = COSE.new()
encoded = sender.encode(
    b"Hello world!",
    mac_key,
    protected={"alg": "HS256"},
    unprotected={"kid": "01"},
)

# The recipient side:
recipient = COSE.new()
assert b"Hello world!" == recipient.decode(encoded, mac_key)

Following two samples are other ways of writing the above example.

CBOR object can be used for protected and unprotected header parameters as follows:

from cwt import COSE, COSEHeaders, COSEKey

mac_key = COSEKey.generate_symmetric_key(alg="HS256", kid="01")

# The sender side:
sender = COSE.new()
encoded = sender.encode(
    b"Hello world!",
    mac_key,
    protected={COSEHeaders.ALG: 5},
    unprotected={COSEHeaders.KID: b"01"},
)

# The recipient side:
recipient = COSE.new()
assert b"Hello world!" == recipient.decode(encoded, mac_key)

alg_auto_inclusion and kid_auto_inclusion can be used to omit to specify alg and kid header parameters respectively as follows:

from cwt import COSE, COSEKey

mac_key = COSEKey.generate_symmetric_key(alg="HS256", kid="01")

# The sender side:
sender = COSE.new(alg_auto_inclusion=True, kid_auto_inclusion=True)
encoded = sender.encode(
    b"Hello world!",
    mac_key,
    # protected={"alg": "HS256"},
    # unprotected={"kid": "01"},
)

# The recipient side:
recipient = COSE.new()
assert b"Hello world!" == recipient.decode(encoded, mac_key)

Countersign (MAC0)

python-cwt supports RFC9338: COSE Countersignatures. The notary below adds a countersignature to a MACed COSE message. The recipinet has to call counterverify to verify the countersignature explicitly.

from cwt import COSE, COSEKey, COSEMessage

mac_key = COSEKey.generate_symmetric_key(alg="HS256", kid="01")

# The sender side:
sender = COSE.new(alg_auto_inclusion=True, kid_auto_inclusion=True)
encoded = sender.encode(b"Hello world!", mac_key)

# The notary side:
notary = Signer.from_jwk(
    {
        "kid": "01",
        "kty": "OKP",
        "crv": "Ed25519",
        "alg": "EdDSA",
        "x": "2E6dX83gqD_D0eAmqnaHe1TC1xuld6iAKXfw2OVATr0",
        "d": "L8JS08VsFZoZxGa9JvzYmCWOwg7zaKcei3KZmYsj7dc",
    },
)
countersigned = COSEMessage.loads(encoded).countersign(notary).dumps()

# The recipient side:
pub_key = COSEKey.from_jwk(
    {
        "kid": "01",
        "kty": "OKP",
        "crv": "Ed25519",
        "alg": "EdDSA",
        "x": "2E6dX83gqD_D0eAmqnaHe1TC1xuld6iAKXfw2OVATr0",
    },
)
recipient = COSE.new()
assert b"Hello world!" == recipient.decode(countersigned, mac_key)
try:
    sig = COSEMessage.loads(countersigned).counterverify(pub_key)
except Exception as err:
    pytest.fail(f"failed to verify: {err}")
countersignature = COSEMessage.from_cose_signature(sig)
assert countersignature.protected[1] == -8  # alg: "EdDSA"
assert countersignature.unprotected[4] == b"01"  # kid: b"01"

COSE MAC

Direct Key Distribution for MAC

The direct key distribution shares a MAC key between the sender and the recipient that is used directly. The follwing example shows the simplest way to make a COSE MAC message, verify and decode it with the direct key distribution method.

from cwt import COSE, COSEKey, Recipient

mac_key = COSEKey.generate_symmetric_key(alg="HS512", kid="01")

# The sender side:
r = Recipient.new(unprotected={"alg": "direct", "kid": mac_key.kid})

sender = COSE.new()
encoded = sender.encode(
    b"Hello world!", mac_key, protected={"alg": "HS512"}, recipients=[r]
)

# The recipient side:
recipient = COSE.new()
assert b"Hello world!" == recipient.decode(encoded, mac_key)

Direct Key with KDF for MAC

from secrets import token_bytes
from cwt import COSE, COSEKey, Recipient

shared_material = token_bytes(32)
shared_key = COSEKey.from_symmetric_key(shared_material, kid="01")

# The sender side:
r = Recipient.new(
    unprotected={
        "alg": "direct+HKDF-SHA-256",
        "salt": "aabbccddeeffgghh",
    },
    context={"alg": "HS256"},
)
sender = COSE.new(alg_auto_inclusion=True)
encoded = sender.encode(
    b"Hello world!",
    shared_key,
    recipients=[r],
)

# The recipient side:
recipient = COSE.new()
assert b"Hello world!" == recipient.decode(
    encoded, shared_key, context={"alg": "HS256"}
)

AES Key Wrap for MAC

The AES key wrap algorithm can be used to wrap a MAC key as follows:

from cwt import COSE, COSEKey, Recipient

enc_key = COSEKey.from_jwk(
    {
        "kty": "oct",
        "kid": "01",
        "alg": "A128KW",
        "k": "hJtXIZ2uSN5kbQfbtTNWbg",  # A shared wrapping key
    }
)

# The sender side:
mac_key = COSEKey.generate_symmetric_key(alg="HS512")
r = Recipient.new(unprotected={"alg": "A128KW"}, sender_key=enc_key)
sender = COSE.new(alg_auto_inclusion=True)
encoded = sender.encode(b"Hello world!", mac_key, recipients=[r])

# The recipient side:
recipient = COSE.new()
assert b"Hello world!" == recipient.decode(encoded, enc_key)

Direct Key Agreement for MAC

The direct key agreement methods can be used to create a shared secret. A KDF (Key Distribution Function) is then applied to the shared secret to derive a key to be used to protect the data. The follwing example shows a simple way to make a COSE Encrypt message, verify and decode it with the direct key agreement methods.

from cwt import COSE, COSEKey, Recipient

# The sender side:
# The following key is provided by the recipient in advance.
pub_key = COSEKey.from_jwk(
    {
        "kty": "EC",
        "kid": "01",
        "crv": "P-256",
        "x": "Ze2loSV3wrroKUN_4zhwGhCqo3Xhu1td4QjeQ5wIVR0",
        "y": "HlLtdXARY_f55A3fnzQbPcm6hgr34Mp8p-nuzQCE0Zw",
    }
)
r = Recipient.new(
    unprotected={"alg": "ECDH-ES+HKDF-256"},
    recipient_key=pub_key,
    context={"alg": "HS256"},
)
sender = COSE.new()
encoded = sender.encode(
    b"Hello world!",
    protected={"alg": "HS256"},
    recipients=[r],
)

# The recipient side:
# The following key is the private key of the above pub_key.
priv_key = COSEKey.from_jwk(
    {
        "kty": "EC",
        "alg": "ECDH-ES+HKDF-256",
        "kid": "01",
        "crv": "P-256",
        "x": "Ze2loSV3wrroKUN_4zhwGhCqo3Xhu1td4QjeQ5wIVR0",
        "y": "HlLtdXARY_f55A3fnzQbPcm6hgr34Mp8p-nuzQCE0Zw",
        "d": "r_kHyZ-a06rmxM3yESK84r1otSg-aQcVStkRhA-iCM8",
    }
)
recipient = COSE.new()
# The enc_key will be derived in decode() with priv_key and
# the sender's public key which is conveyed as the recipient
# information structure in the COSE Encrypt message (encoded).
assert b"Hello world!" == recipient.decode(encoded, priv_key, context={"alg": "HS256"})

Key Agreement with Key Wrap for MAC

from cwt import COSE, COSEKey, Recipient

# The sender side:
mac_key = COSEKey.generate_symmetric_key(alg="HS256")
pub_key = COSEKey.from_jwk(
    {
        "kty": "EC",
        "alg": "ECDH-ES+A128KW",
        "kid": "01",
        "crv": "P-256",
        "x": "Ze2loSV3wrroKUN_4zhwGhCqo3Xhu1td4QjeQ5wIVR0",
        "y": "HlLtdXARY_f55A3fnzQbPcm6hgr34Mp8p-nuzQCE0Zw",
    }
)
r = Recipient.new(
    unprotected={"alg": "ECDH-ES+A128KW"},
    recipient_key=pub_key,
    context={"alg": "HS256"},
)
sender = COSE.new(alg_auto_inclusion=True)
encoded = sender.encode(
    b"Hello world!",
    mac_key,
    recipients=[r],
)

# The recipient side:
recipient = COSE.new()
priv_key = COSEKey.from_jwk(
    {
        "kty": "EC",
        "alg": "ECDH-ES+A128KW",
        "kid": "01",
        "crv": "P-256",
        "x": "Ze2loSV3wrroKUN_4zhwGhCqo3Xhu1td4QjeQ5wIVR0",
        "y": "HlLtdXARY_f55A3fnzQbPcm6hgr34Mp8p-nuzQCE0Zw",
        "d": "r_kHyZ-a06rmxM3yESK84r1otSg-aQcVStkRhA-iCM8",
    }
)
assert b"Hello world!" == recipient.decode(encoded, priv_key, context={"alg": "HS256"})

Countersign (MAC)

python-cwt supports RFC9338: COSE Countersignatures. The notary below adds a countersignature to a MACed COSE message. The recipinet has to call counterverify to verify the countersignature explicitly.

from cwt import COSE, COSEKey, COSEMessage, Recipient

mac_key = COSEKey.generate_symmetric_key(alg="HS256", kid="01")

# The sender side:
r = Recipient.new(unprotected={"alg": "direct", "kid": mac_key.kid})
sender = COSE.new()
encoded = sender.encode(
    b"Hello world!", mac_key, protected={"alg": "HS256"}, recipients=[r]
)

# The notary side:
notary = Signer.from_jwk(
    {
        "kid": "01",
        "kty": "OKP",
        "crv": "Ed25519",
        "alg": "EdDSA",
        "x": "2E6dX83gqD_D0eAmqnaHe1TC1xuld6iAKXfw2OVATr0",
        "d": "L8JS08VsFZoZxGa9JvzYmCWOwg7zaKcei3KZmYsj7dc",
    },
)
countersigned = COSEMessage.loads(encoded).countersign(notary).dumps()

# The recipient side:
pub_key = COSEKey.from_jwk(
    {
        "kid": "01",
        "kty": "OKP",
        "crv": "Ed25519",
        "alg": "EdDSA",
        "x": "2E6dX83gqD_D0eAmqnaHe1TC1xuld6iAKXfw2OVATr0",
    },
)
recipient = COSE.new()
assert b"Hello world!" == recipient.decode(countersigned, mac_key)
try:
    sig = COSEMessage.loads(countersigned).counterverify(pub_key)
except Exception as err:
    pytest.fail(f"failed to verify: {err}")
countersignature = COSEMessage.from_cose_signature(sig)
assert countersignature.protected[1] == -8  # alg: "EdDSA"
assert countersignature.unprotected[4] == b"01"  # kid: b"01"

COSE-HPKE (MAC)

Experimental Implementation. DO NOT USE for production.

Create a COSE-HPKE MAC message, verify and decode it as follows:

from cwt import COSE, COSEAlgs, COSEHeaders, COSEKey, Recipient

# The sender side:
mac_key = COSEKey.generate_symmetric_key(alg="HS256")
rpk = COSEKey.from_jwk(
    {
        "kty": "EC",
        "kid": "01",
        "crv": "P-256",
        "x": "usWxHK2PmfnHKwXPS54m0kTcGJ90UiglWiGahtagnv8",
        "y": "IBOL-C3BttVivg-lSreASjpkttcsz-1rb7btKLv8EX4",
    }
)
r = Recipient.new(
    protected={
        COSEHeaders.ALG: COSEAlgs.HPKE_BASE_P256_SHA256_AES128GCM,
    },
    unprotected={
        COSEHeaders.KID: b"01",  # kid: "01"
    },
    recipient_key=rpk,
)
sender = COSE.new()
encoded = sender.encode(
    b"This is the content.",
    mac_key,
    protected={COSEHeaders.ALG: COSEAlgs.HS256},
    recipients=[r],
)

# The recipient side:
rsk = COSEKey.from_jwk(
    {
        "kty": "EC",
        "kid": "01",
        "crv": "P-256",
        "x": "usWxHK2PmfnHKwXPS54m0kTcGJ90UiglWiGahtagnv8",
        "y": "IBOL-C3BttVivg-lSreASjpkttcsz-1rb7btKLv8EX4",
        "d": "V8kgd2ZBRuh2dgyVINBUqpPDr7BOMGcF22CQMIUHtNM",
    }
)
recipient = COSE.new()
assert b"This is the content." == recipient.decode(encoded, rsk)

COSE Encrypt0

Encryption with ChaCha20/Poly1305

Create a COSE Encrypt0 message and decrypt it as follows:

from cwt import COSE, COSEKey

enc_key = COSEKey.generate_symmetric_key(alg="ChaCha20/Poly1305", kid="01")

# The sender side:
nonce = enc_key.generate_nonce()
sender = COSE.new(alg_auto_inclusion=True, kid_auto_inclusion=True)
encoded = sender.encode(b"Hello world!", enc_key, unprotected={COSEHeaders.IV: nonce})

# The recipient side:
recipient = COSE.new()
assert b"Hello world!" == recipient.decode(encoded, enc_key)

The following sample is another way of writing the above:

from cwt import COSE, COSEKey

enc_key = COSEKey.generate_symmetric_key(alg="ChaCha20/Poly1305", kid="01")

# The sender side:
nonce = enc_key.generate_nonce()
sender = COSE.new()
encoded = sender.encode(
    b"Hello world!",
    enc_key,
    protected={"alg": "ChaCha20/Poly1305"},
    unprotected={"kid": "01", "iv": nonce},
)

# The recipient side:
recipient = COSE.new()
assert b"Hello world!" == recipient.decode(encoded, enc_key)

Countersign (Encrypt0)

python-cwt supports RFC9338: COSE Countersignatures. The notary below adds a countersignature to an encrypted COSE message. The recipinet has to call counterverify to verify the countersignature explicitly.

from cwt import COSE, COSEKey, COSEMessage

enc_key = COSEKey.generate_symmetric_key(alg="ChaCha20/Poly1305", kid="01")

# The sender side:
nonce = enc_key.generate_nonce()
sender = COSE.new(alg_auto_inclusion=True, kid_auto_inclusion=True)
encoded = sender.encode(b"Hello world!", enc_key, unprotected={COSEHeaders.IV: nonce})

# The notary side:
notary = Signer.from_jwk(
    {
        "kid": "01",
        "kty": "OKP",
        "crv": "Ed25519",
        "alg": "EdDSA",
        "x": "2E6dX83gqD_D0eAmqnaHe1TC1xuld6iAKXfw2OVATr0",
        "d": "L8JS08VsFZoZxGa9JvzYmCWOwg7zaKcei3KZmYsj7dc",
    },
)
countersigned = COSEMessage.loads(encoded).countersign(notary).dumps()

# The recipient side:
pub_key = COSEKey.from_jwk(
    {
        "kid": "01",
        "kty": "OKP",
        "crv": "Ed25519",
        "alg": "EdDSA",
        "x": "2E6dX83gqD_D0eAmqnaHe1TC1xuld6iAKXfw2OVATr0",
    },
)
recipient = COSE.new()
assert b"Hello world!" == recipient.decode(countersigned, enc_key)
try:
    sig = COSEMessage.loads(countersigned).counterverify(pub_key)
except Exception as err:
    pytest.fail(f"failed to verify: {err}")
countersignature = COSEMessage.from_cose_signature(sig)
assert countersignature.protected[1] == -8  # alg: "EdDSA"
assert countersignature.unprotected[4] == b"01"  # kid: b"01"

COSE-HPKE (Encrypt0)

Experimental Implementation. DO NOT USE for production.

Create a COSE-HPKE Encrypt0 message and decrypt it as follows:

from cwt import COSE, COSEAlgs, COSEHeaders, COSEKey

# The sender side:
rpk = COSEKey.from_jwk(
    {
        "kty": "EC",
        "kid": "01",
        "crv": "P-256",
        "x": "usWxHK2PmfnHKwXPS54m0kTcGJ90UiglWiGahtagnv8",
        "y": "IBOL-C3BttVivg-lSreASjpkttcsz-1rb7btKLv8EX4",
    }
)

sender = COSE.new()
encoded = sender.encode(
    b"This is the content.",
    rpk,
    protected={
        COSEHeaders.ALG: COSEAlgs.HPKE_BASE_P256_SHA256_AES128GCM,
    },
    unprotected={
        COSEHeaders.KID: b"01",  # kid: "01"
    },
)

# The recipient side:
rsk = COSEKey.from_jwk(
    {
        "kty": "EC",
        "kid": "01",
        "crv": "P-256",
        "x": "usWxHK2PmfnHKwXPS54m0kTcGJ90UiglWiGahtagnv8",
        "y": "IBOL-C3BttVivg-lSreASjpkttcsz-1rb7btKLv8EX4",
        "d": "V8kgd2ZBRuh2dgyVINBUqpPDr7BOMGcF22CQMIUHtNM",
    }
)
recipient = COSE.new()
assert b"This is the content." == recipient.decode(encoded, rsk)

COSE Encrypt

Direct Key Distribution for encryption

The direct key distribution shares a MAC key between the sender and the recipient that is used directly. The follwing example shows the simplest way to make a COSE MAC message, verify and decode it with the direct key distribution method.

from cwt import COSE, COSEHeaders, COSEKey, Recipient

enc_key = COSEKey.generate_symmetric_key(alg="ChaCha20/Poly1305", kid="01")

# The sender side:
nonce = enc_key.generate_nonce()
r = Recipient.new(unprotected={"alg": "direct"})
# r = Recipient.new(unprotected={COSEHeaders.ALG: -6}) # is also acceptable.

sender = COSE.new()
encoded = sender.encode(
    b"Hello world!",
    enc_key,
    protected={"alg": "ChaCha20/Poly1305"},
    # protected={COSEHeaders.ALG: 24},  # is also acceptable.
    unprotected={"kid": enc_key.kid, "iv": nonce},
    # unprotected={COSEHeaders.KID: enc_key.kid, COSEHeaders.IV: nonce},  # is also acceptable.
    recipients=[r],
)

# The recipient side:
recipient = COSE.new()
assert b"Hello world!" == recipient.decode(encoded, enc_key)

Direct Key with KDF for encryption

from cwt import COSE, COSEKey, Recipient

shared_material = token_bytes(32)
shared_key = COSEKey.from_symmetric_key(shared_material, kid="01")

# The sender side:
r = Recipient.new(
    unprotected={
        "alg": "direct+HKDF-SHA-256",
        "salt": "aabbccddeeffgghh",
    },
    context={"alg": "A256GCM"},
)
sender = COSE.new(alg_auto_inclusion=True)
encoded = sender.encode(
    b"Hello world!",
    shared_key,
    recipients=[r],
)

# The recipient side:
recipient = COSE.new()
assert b"Hello world!" == recipient.decode(
    encoded, shared_key, context={"alg": "A256GCM"}
)

AES Key Wrap for encryption

The AES key wrap algorithm can be used to wrap a MAC key as follows:

from cwt import COSE, COSEKey, Recipient

wrapping_key = COSEKey.from_jwk(
    {
        "kty": "oct",
        "alg": "A128KW",
        "kid": "01",
        "k": "hJtXIZ2uSN5kbQfbtTNWbg",  # A shared wrapping key
    }
)

# The sender side:
enc_key = COSEKey.generate_symmetric_key(alg="ChaCha20/Poly1305")
r = Recipient.new(
    unprotected={"alg": "A128KW"},
    sender_key=wrapping_key,
)
sender = COSE.new(alg_auto_inclusion=True)
encoded = sender.encode(b"Hello world!", key=enc_key, recipients=[r])

# The recipient side:
recipient = COSE.new()
assert b"Hello world!" == recipient.decode(encoded, wrapping_key)

Direct Key Agreement for encryption

The direct key agreement methods can be used to create a shared secret. A KDF (Key Distribution Function) is then applied to the shared secret to derive a key to be used to protect the data. The follwing example shows a simple way to make a COSE Encrypt message, verify and decode it with the direct key agreement methods.

from cwt import COSE, COSEKey, Recipient

# The sender side:
pub_key = COSEKey.from_jwk(
    {
        "kty": "EC",
        "kid": "01",
        "crv": "P-256",
        "x": "Ze2loSV3wrroKUN_4zhwGhCqo3Xhu1td4QjeQ5wIVR0",
        "y": "HlLtdXARY_f55A3fnzQbPcm6hgr34Mp8p-nuzQCE0Zw",
    }
)
r = Recipient.new(
    unprotected={"alg": "ECDH-ES+HKDF-256"},
    recipient_key=pub_key,
    context={"alg": "A128GCM"},
)
sender = COSE.new(alg_auto_inclusion=True)
encoded = sender.encode(
    b"Hello world!",
    recipients=[r],
)

# The recipient side:
recipient = COSE.new()
priv_key = COSEKey.from_jwk(
    {
        "kty": "EC",
        "alg": "ECDH-ES+HKDF-256",
        "kid": "01",
        "crv": "P-256",
        "x": "Ze2loSV3wrroKUN_4zhwGhCqo3Xhu1td4QjeQ5wIVR0",
        "y": "HlLtdXARY_f55A3fnzQbPcm6hgr34Mp8p-nuzQCE0Zw",
        "d": "r_kHyZ-a06rmxM3yESK84r1otSg-aQcVStkRhA-iCM8",
    }
)
assert b"Hello world!" == recipient.decode(
    encoded, priv_key, context={"alg": "A128GCM"}
)

Key Agreement with Key Wrap for encryption

from cwt import COSE, COSEKey, Recipient

# The sender side:
enc_key = COSEKey.generate_symmetric_key(alg="A128GCM")
nonce = enc_key.generate_nonce()
r_pub_key = COSEKey.from_jwk(
    {
        "kty": "EC",
        "crv": "P-256",
        "kid": "[e-mail]",
        "x": "Ze2loSV3wrroKUN_4zhwGhCqo3Xhu1td4QjeQ5wIVR0",
        "y": "HlLtdXARY_f55A3fnzQbPcm6hgr34Mp8p-nuzQCE0Zw",
    }
)
s_priv_key = COSEKey.from_jwk(
    {
        "kty": "EC",
        "crv": "P-256",
        "alg": "ECDH-SS+A128KW",
        "x": "7cvYCcdU22WCwW1tZXR8iuzJLWGcd46xfxO1XJs-SPU",
        "y": "DzhJXgz9RI6TseNmwEfLoNVns8UmvONsPzQDop2dKoo",
        "d": "Uqr4fay_qYQykwcNCB2efj_NFaQRRQ-6fHZm763jt5w",
    }
)
r = Recipient.new(
    unprotected={"alg": "ECDH-SS+A128KW"},
    sender_key=s_priv_key,
    recipient_key=r_pub_key,
    context={"alg": "A128GCM"},
)
sender = COSE.new(alg_auto_inclusion=True)
encoded = sender.encode(
    b"Hello world!",
    key=enc_key,
    unprotected={COSEHeaders.IV: nonce},
    recipients=[r],
)

# The recipient side:
recipient = COSE.new()
r_priv_key = COSEKey.from_jwk(
    {
        "kty": "EC",
        "crv": "P-256",
        "alg": "ECDH-SS+A128KW",
        "kid": "[e-mail]",
        "x": "Ze2loSV3wrroKUN_4zhwGhCqo3Xhu1td4QjeQ5wIVR0",
        "y": "HlLtdXARY_f55A3fnzQbPcm6hgr34Mp8p-nuzQCE0Zw",
        "d": "r_kHyZ-a06rmxM3yESK84r1otSg-aQcVStkRhA-iCM8",
    }
)
assert b"Hello world!" == recipient.decode(
    encoded, r_priv_key, context={"alg": "A128GCM"}
)

Countersign (Encrypt)

python-cwt supports RFC9338: COSE Countersignatures. The notary below adds a countersignature to an encrypted COSE message. The recipinet has to call counterverify to verify the countersignature explicitly.

from cwt import COSE, COSEKey, COSEMessage, Recipient

enc_key = COSEKey.generate_symmetric_key(alg="ChaCha20/Poly1305", kid="01")

# The sender side:
nonce = enc_key.generate_nonce()
r = Recipient.new(unprotected={"alg": "direct"})

sender = COSE.new()
encoded = sender.encode(
    b"Hello world!",
    enc_key,
    protected={"alg": "ChaCha20/Poly1305"},
    unprotected={"kid": enc_key.kid, "iv": nonce},
    recipients=[r],
)

# The notary side:
notary = Signer.from_jwk(
    {
        "kid": "01",
        "kty": "OKP",
        "crv": "Ed25519",
        "alg": "EdDSA",
        "x": "2E6dX83gqD_D0eAmqnaHe1TC1xuld6iAKXfw2OVATr0",
        "d": "L8JS08VsFZoZxGa9JvzYmCWOwg7zaKcei3KZmYsj7dc",
    },
)
countersigned = COSEMessage.loads(encoded).countersign(notary).dumps()

# The recipient side:
pub_key = COSEKey.from_jwk(
    {
        "kid": "01",
        "kty": "OKP",
        "crv": "Ed25519",
        "alg": "EdDSA",
        "x": "2E6dX83gqD_D0eAmqnaHe1TC1xuld6iAKXfw2OVATr0",
    },
)
recipient = COSE.new()
assert b"Hello world!" == recipient.decode(countersigned, enc_key)

try:
    sig = COSEMessage.loads(countersigned).counterverify(pub_key)
except Exception as err:
    pytest.fail(f"failed to verify: {err}")
countersignature = COSEMessage.from_cose_signature(sig)
assert countersignature.protected[1] == -8  # alg: "EdDSA"
assert countersignature.unprotected[4] == b"01"  # kid: b"01"

COSE-HPKE (Encrypt)

Experimental Implementation. DO NOT USE for production.

Create a COSE-HPKE Encrypt message and decrypt it as follows:

from cwt import COSE, COSEAlgs, COSEHeaders, COSEKey, Recipient

# The sender side:
enc_key = COSEKey.generate_symmetric_key(alg="A128GCM")
rpk = COSEKey.from_jwk(
    {
        "kty": "EC",
        "kid": "01",
        "crv": "P-256",
        "x": "usWxHK2PmfnHKwXPS54m0kTcGJ90UiglWiGahtagnv8",
        "y": "IBOL-C3BttVivg-lSreASjpkttcsz-1rb7btKLv8EX4",
    }
)
r = Recipient.new(
    protected={
        COSEHeaders.ALG: COSEAlgs.HPKE_BASE_P256_SHA256_AES128GCM,
    },
    unprotected={
        COSEHeaders.KID: b"01",  # kid: "01"
    },
    recipient_key=rpk,
)
sender = COSE.new()
encoded = sender.encode(
    b"This is the content.",
    enc_key,
    protected={
        COSEHeaders.ALG: 1,  # alg: "A128GCM"
    },
    recipients=[r],
)

# The recipient side:
rsk = COSEKey.from_jwk(
    {
        "kty": "EC",
        "kid": "01",
        "crv": "P-256",
        "x": "usWxHK2PmfnHKwXPS54m0kTcGJ90UiglWiGahtagnv8",
        "y": "IBOL-C3BttVivg-lSreASjpkttcsz-1rb7btKLv8EX4",
        "d": "V8kgd2ZBRuh2dgyVINBUqpPDr7BOMGcF22CQMIUHtNM",
    }
)
recipient = COSE.new()
assert b"This is the content." == recipient.decode(encoded, rsk)

COSE Signature1

Sign1 with EC P-256

Create a COSE Signature1 message, verify and decode it as follows:

from cwt import COSE, COSEKey, Signer

# The sender side:
priv_key = COSEKey.from_jwk(
    {
        "kty": "EC",
        "kid": "01",
        "crv": "P-256",
        "x": "usWxHK2PmfnHKwXPS54m0kTcGJ90UiglWiGahtagnv8",
        "y": "IBOL-C3BttVivg-lSreASjpkttcsz-1rb7btKLv8EX4",
        "d": "V8kgd2ZBRuh2dgyVINBUqpPDr7BOMGcF22CQMIUHtNM",
    }
)
sender = COSE.new(alg_auto_inclusion=True, kid_auto_inclusion=True)
encoded = sender.encode(b"Hello world!", priv_key)

# The recipient side:
pub_key = COSEKey.from_jwk(
    {
        "kty": "EC",
        "kid": "01",
        "crv": "P-256",
        "x": "usWxHK2PmfnHKwXPS54m0kTcGJ90UiglWiGahtagnv8",
        "y": "IBOL-C3BttVivg-lSreASjpkttcsz-1rb7btKLv8EX4",
    }
)
recipient = COSE.new()
assert b"Hello world!" == recipient.decode(encoded, pub_key)

Countersign (Sign1)

python-cwt supports RFC9338: COSE Countersignatures. The notary below adds a countersignature to a signed COSE message. The recipinet has to call counterverify to verify the countersignature explicitly.

from cwt import COSE, COSEKey, COSEMessage

# The sender side:
priv_key = COSEKey.from_jwk(
    {
        "kty": "EC",
        "kid": "01",
        "crv": "P-256",
        "x": "usWxHK2PmfnHKwXPS54m0kTcGJ90UiglWiGahtagnv8",
        "y": "IBOL-C3BttVivg-lSreASjpkttcsz-1rb7btKLv8EX4",
        "d": "V8kgd2ZBRuh2dgyVINBUqpPDr7BOMGcF22CQMIUHtNM",
    }
)
sender = COSE.new(alg_auto_inclusion=True, kid_auto_inclusion=True)
encoded = sender.encode(b"Hello world!", priv_key)

# The notary side:
notary = Signer.from_jwk(
    {
        "kid": "01",
        "kty": "OKP",
        "crv": "Ed25519",
        "alg": "EdDSA",
        "x": "2E6dX83gqD_D0eAmqnaHe1TC1xuld6iAKXfw2OVATr0",
        "d": "L8JS08VsFZoZxGa9JvzYmCWOwg7zaKcei3KZmYsj7dc",
    },
)
countersigned = COSEMessage.loads(encoded).countersign(notary).dumps()

# The recipient side:
pub_key = COSEKey.from_jwk(
    {
        "kty": "EC",
        "kid": "01",
        "crv": "P-256",
        "x": "usWxHK2PmfnHKwXPS54m0kTcGJ90UiglWiGahtagnv8",
        "y": "IBOL-C3BttVivg-lSreASjpkttcsz-1rb7btKLv8EX4",
    }
)
notary_pub_key = COSEKey.from_jwk(
    {
        "kid": "01",
        "kty": "OKP",
        "crv": "Ed25519",
        "alg": "EdDSA",
        "x": "2E6dX83gqD_D0eAmqnaHe1TC1xuld6iAKXfw2OVATr0",
    },
)
recipient = COSE.new()
assert b"Hello world!" == recipient.decode(countersigned, pub_key)
try:
    sig = COSEMessage.loads(countersigned).counterverify(notary_pub_key)
except Exception as err:
    pytest.fail(f"failed to verify: {err}")
countersignature = COSEMessage.from_cose_signature(sig)
assert countersignature.protected[1] == -8  # alg: "EdDSA"
assert countersignature.unprotected[4] == b"01"  # kid: b"01"

COSE Signature

Sign with EC P-256

Create a COSE Signature message, verify and decode it as follows:

from cwt import COSE, COSEKey, Signer

# The sender side:
signer = Signer.from_jwk(
    {
        "kty": "EC",
        "kid": "01",
        "crv": "P-256",
        "x": "usWxHK2PmfnHKwXPS54m0kTcGJ90UiglWiGahtagnv8",
        "y": "IBOL-C3BttVivg-lSreASjpkttcsz-1rb7btKLv8EX4",
        "d": "V8kgd2ZBRuh2dgyVINBUqpPDr7BOMGcF22CQMIUHtNM",
    },
)
sender = COSE.new()
encoded = sender.encode(b"Hello world!", signers=[signer])

# The recipient side:
recipient = COSE.new()
pub_key = COSEKey.from_jwk(
    {
        "kty": "EC",
        "kid": "01",
        "crv": "P-256",
        "x": "usWxHK2PmfnHKwXPS54m0kTcGJ90UiglWiGahtagnv8",
        "y": "IBOL-C3BttVivg-lSreASjpkttcsz-1rb7btKLv8EX4",
    }
)
assert b"Hello world!" == recipient.decode(encoded, pub_key)

Countersign (Sign)

python-cwt supports RFC9338: COSE Countersignatures. The notary below adds a countersignature to a signed COSE message. The recipinet has to call counterverify to verify the countersignature explicitly.

from cwt import COSE, COSEKey, COSEMessage, Signer

# The sender side:
signer = Signer.from_jwk(
    {
        "kty": "EC",
        "kid": "01",
        "crv": "P-256",
        "x": "usWxHK2PmfnHKwXPS54m0kTcGJ90UiglWiGahtagnv8",
        "y": "IBOL-C3BttVivg-lSreASjpkttcsz-1rb7btKLv8EX4",
        "d": "V8kgd2ZBRuh2dgyVINBUqpPDr7BOMGcF22CQMIUHtNM",
    },
)
sender = COSE.new()
encoded = sender.encode(b"Hello world!", signers=[signer])

# The notary side:
notary = Signer.from_jwk(
    {
        "kid": "01",
        "kty": "OKP",
        "crv": "Ed25519",
        "alg": "EdDSA",
        "x": "2E6dX83gqD_D0eAmqnaHe1TC1xuld6iAKXfw2OVATr0",
        "d": "L8JS08VsFZoZxGa9JvzYmCWOwg7zaKcei3KZmYsj7dc",
    },
)
countersigned = COSEMessage.loads(encoded).countersign(notary).dumps()

# The recipient side:
pub_key = COSEKey.from_jwk(
    {
        "kty": "EC",
        "kid": "01",
        "crv": "P-256",
        "x": "usWxHK2PmfnHKwXPS54m0kTcGJ90UiglWiGahtagnv8",
        "y": "IBOL-C3BttVivg-lSreASjpkttcsz-1rb7btKLv8EX4",
    }
)
notary_pub_key = COSEKey.from_jwk(
    {
        "kid": "01",
        "kty": "OKP",
        "crv": "Ed25519",
        "alg": "EdDSA",
        "x": "2E6dX83gqD_D0eAmqnaHe1TC1xuld6iAKXfw2OVATr0",
    },
)
recipient = COSE.new()
assert b"Hello world!" == recipient.decode(encoded, pub_key)

try:
    sig = COSEMessage.loads(countersigned).counterverify(notary_pub_key)
except Exception as err:
    pytest.fail(f"failed to verify: {err}")
countersignature = COSEMessage.from_cose_signature(sig)
assert countersignature.protected[1] == -8  # alg: "EdDSA"
assert countersignature.unprotected[4] == b"01"  # kid: b"01"

CWT Usage Examples

Followings are typical and basic examples which encode various types of CWTs, verify and decode them.

CWT API in the examples are built on top of COSE API.

See API Reference.

MACed CWT

Create a MACed CWT with HS256, verify and decode it as follows:

import cwt
from cwt import Claims, COSEKey

try:
    key = COSEKey.generate_symmetric_key(alg="HS256", kid="01")
    token = cwt.encode(
        {"iss": "coaps://as.example", "sub": "dajiaji", "cti": "123"}, key
    )
    decoded = cwt.decode(token, key)

    # If you want to treat the result like a JWT;
    readable = Claims.new(decoded)
    assert readable.iss == "coaps://as.example"
    assert readable.sub == "dajiaji"
    assert readable.cti == "123"
    # readable.exp == 1620088759
    # readable.nbf == 1620085159
    # readable.iat == 1620085159

except Exception as err:
    # All the other examples in this document omit error handling but this CWT library
    # can throw following errors:
    #   ValueError: Invalid arguments.
    #   EncodeError: Failed to encode.
    #   VerifyError: Failed to verify.
    #   DecodeError: Failed to decode.
    print(err)

A raw CWT structure (Dict[int, Any]) can also be used as follows:

import cwt
from cwt import COSEKey, CWTClaims

key = COSEKey.generate_symmetric_key(alg="HS256", kid="01")
token = cwt.encode(
    {
        CWTClaims.ISS: "coaps://as.example",
        CWTClaims.SUB: "dajiaji",
        CWTClaims.CTI: b"123",
    },
    key,
)
decoded = cwt.decode(token, key)

MAC algorithms other than HS256 are listed in Supported COSE Algorithms.

Signed CWT

Create an Ed25519 key pair:

$ openssl genpkey -algorithm ed25519 -out private_key.pem
$ openssl pkey -in private_key.pem -pubout -out public_key.pem

Create a Signed CWT with Ed25519, verify and decode it with the key pair as follows:

import cwt
from cwt import COSEKey

# The sender side:
with open("./private_key.pem") as key_file:
    private_key = COSEKey.from_pem(key_file.read(), kid="01")
token = cwt.encode(
    {"iss": "coaps://as.example", "sub": "dajiaji", "cti": "123"}, private_key
)

# The recipient side:
with open("./public_key.pem") as key_file:
    public_key = COSEKey.from_pem(key_file.read(), kid="01")
decoded = cwt.decode(token, public_key)

JWKs can also be used instead of the PEM-formatted keys as follows:

import cwt
from cwt import COSEKey

# The sender side:
private_key = COSEKey.from_jwk(
    {
        "kid": "01",
        "kty": "OKP",
        "key_ops": ["sign"],
        "alg": "EdDSA",
        "crv": "Ed25519",
        "x": "2E6dX83gqD_D0eAmqnaHe1TC1xuld6iAKXfw2OVATr0",
        "d": "L8JS08VsFZoZxGa9JvzYmCWOwg7zaKcei3KZmYsj7dc",
    }
)
token = cwt.encode(
    {"iss": "coaps://as.example", "sub": "dajiaji", "cti": "123"}, private_key
)

# The recipient side:
public_key = COSEKey.from_jwk(
    {
        "kid": "01",
        "kty": "OKP",
        "key_ops": ["verify"],
        "crv": "Ed25519",
        "x": "2E6dX83gqD_D0eAmqnaHe1TC1xuld6iAKXfw2OVATr0",
    }
)
decoded = cwt.decode(token, public_key)

Signing algorithms other than Ed25519 are listed in Supported COSE Algorithms.

Encrypted CWT

Create an encrypted CWT with ChaCha20/Poly1305 and decrypt it as follows:

import cwt
from cwt import COSEKey

enc_key = COSEKey.generate_symmetric_key(alg="ChaCha20/Poly1305", kid="01")
token = cwt.encode(
    {"iss": "coaps://as.example", "sub": "dajiaji", "cti": "123"}, enc_key
)
decoded = cwt.decode(token, enc_key)

Encryption algorithms other than ChaCha20/Poly1305 are listed in Supported COSE Algorithms.

Nested CWT

Create a signed CWT and encrypt it, and then decrypt and verify the nested CWT as follows.

import cwt
from cwt import COSEKey

# A shared encryption key.
enc_key = COSEKey.generate_symmetric_key(alg="ChaCha20/Poly1305", kid="enc-01")

# Creates a CWT with ES256 signing.
with open("./private_key.pem") as key_file:
    private_key = COSEKey.from_pem(key_file.read(), kid="sig-01")
token = cwt.encode(
    {"iss": "coaps://as.example", "sub": "dajiaji", "cti": "123"}, private_key
)

# Encrypts the signed CWT.
nested = cwt.encode(token, enc_key)

# Decrypts and verifies the nested CWT.
with open("./public_key.pem") as key_file:
    public_key = COSEKey.from_pem(key_file.read(), kid="sig-01")
decoded = cwt.decode(nested, [enc_key, public_key])

CWT with User Settings

The cwt in cwt.encode() and cwt.decode() above is a global CWT class instance created with default settings in advance. The default settings are as follows:

• expires_in: 3600 seconds. This is the default lifetime in seconds of CWTs.
• leeway: 60 seconds. This is the default leeway in seconds for validating exp and nbf.

If you want to change the settings, you can create your own CWT class instance as follows:

from cwt import COSEKey, CWT

key = COSEKey.generate_symmetric_key(alg="HS256", kid="01")
mycwt = CWT.new(expires_in=3600 * 24, leeway=10)
token = mycwt.encode({"iss": "coaps://as.example", "sub": "dajiaji", "cti": "123"}, key)
decoded = mycwt.decode(token, key)

CWT with User-Defined Claims

You can use your own claims as follows:

Note that such user-defined claim's key should be less than -65536.

import cwt
from cwt import COSEKey, CWTClaims

# The sender side:
with open("./private_key.pem") as key_file:
    private_key = COSEKey.from_pem(key_file.read(), kid="01")
token = cwt.encode(
    {
        CWTClaims.ISS: "coaps://as.example",  # iss
        CWTClaims.SUB: "dajiaji",  # sub
        CWTClaims.CTI: b"123",  # cti
        -70001: "foo",
        -70002: ["bar"],
        -70003: {"baz": "qux"},
        -70004: 123,
    },
    private_key,
)

# The recipient side:
with open("./public_key.pem") as key_file:
    public_key = COSEKey.from_pem(key_file.read(), kid="01")
raw = cwt.decode(token, public_key)
assert raw[-70001] == "foo"
assert raw[-70002][0] == "bar"
assert raw[-70003]["baz"] == "qux"
assert raw[-70004] == 123

readable = Claims.new(raw)
assert readable.get(-70001) == "foo"
assert readable.get(-70002)[0] == "bar"
assert readable.get(-70003)["baz"] == "qux"
assert readable.get(-70004) == 123

User-defined claims can also be used with JSON-based claims as follows:

import cwt
from cwt import Claims, COSEKey

with open("./private_key.pem") as key_file:
    private_key = COSEKey.from_pem(key_file.read(), kid="01")

my_claim_names = {
    "ext_1": -70001,
    "ext_2": -70002,
    "ext_3": -70003,
    "ext_4": -70004,
}

set_private_claim_names(my_claim_names)
token = cwt.encode(
    {
        "iss": "coaps://as.example",
        "sub": "dajiaji",
        "cti": b"123",
        "ext_1": "foo",
        "ext_2": ["bar"],
        "ext_3": {"baz": "qux"},
        "ext_4": 123,
    },
    private_key,
)

with open("./public_key.pem") as key_file:
    public_key = COSEKey.from_pem(key_file.read(), kid="01")

raw = cwt.decode(token, public_key)
readable = Claims.new(
    raw,
    private_claims_names=my_claim_names,
)
assert readable.get("ext_1") == "foo"
assert readable.get("ext_2")[0] == "bar"
assert readable.get("ext_3")["baz"] == "qux"
assert readable.get("ext_4") == 123

CWT with CWT claims in COSE headers

Python CWT supports CWT Claims in COSE Headers experimentally.

If a CWT message has a CWT Claims header parameter in its protected header, cwt.decode() checks whether the values of the claims included in that parameter match the values of the corresponding claims in the payload. If they do not match, VerifyError is raised.

from cwt import COSE, COSEHeaders, COSEKey, CWT, CWTClaims

enc_key = COSEKey.from_symmetric_key(alg="A128GCM", kid="01")

# The sender side:
sender = COSE.new(alg_auto_inclusion=True, kid_auto_inclusion=True)
payload = cbor2.dumps(
    {
        CWTClaims.ISS: "coap://as.example.com",
        CWTClaims.SUB: "erikw",
        CWTClaims.AUD: "coap://light.example.com",
        CWTClaims.EXP: now() + 3600,
        CWTClaims.NBF: now(),
        CWTClaims.IAT: now(),
        CWTClaims.CTI: bytes.fromhex("0b71"),
    },
)
protected = {
    COSEHeaders.CWT_CLAIMS: {  # 13
        CWTClaims.ISS: "coap://as.example.com",
    }
}
token = sender.encode(payload, enc_key, protected)

# The recipient side:
recipient = CWT.new()
# `decode()` checks the validity of the CWT claims header parameter.
decoded = recipient.decode(token, enc_key)
assert decoded[CWTClaims.ISS] == "coap://as.example.com"
assert decoded[CWTClaims.SUB] == "erikw"

CWT with PoP Key

Python CWT supports Proof-of-Possession Key Semantics for CBOR Web Tokens (CWTs). A CWT can include a PoP key as follows:

On the issuer side:

import cwt
from cwt import COSEKey

# Prepares a signing key for CWT in advance.
with open("./private_key_of_issuer.pem") as key_file:
    private_key = COSEKey.from_pem(key_file.read(), kid="issuer-01")

# Sets the PoP key to a CWT for the presenter.
token = cwt.encode(
    {
        "iss": "coaps://as.example",
        "sub": "dajiaji",
        "cti": "123",
        "cnf": {
            "jwk": {  # Provided by the CWT presenter.
                "kty": "OKP",
                "use": "sig",
                "crv": "Ed25519",
                "kid": "presenter-01",
                "x": "2E6dX83gqD_D0eAmqnaHe1TC1xuld6iAKXfw2OVATr0",
                "alg": "EdDSA",
            },
        },
    },
    private_key,
)

# Issues the token to the presenter.

On the CWT presenter side:

import cwt
from cwt import COSEKey

# Prepares a private PoP key in advance.
with open("./private_pop_key.pem") as key_file:
    pop_key_private = COSEKey.from_pem(key_file.read(), kid="presenter-01")

# Receives a message (e.g., nonce)  from the recipient.
msg = b"could-you-sign-this-message?"  # Provided by recipient.

# Signs the message with the private PoP key.
sig = pop_key_private.sign(msg)

# Sends the msg and the sig with the CWT to the recipient.

On the CWT recipient side:

import cwt
from cwt import Claims, COSEKey

# Prepares the public key of the issuer in advance.
with open("./public_key_of_issuer.pem") as key_file:
    public_key = COSEKey.from_pem(key_file.read(), kid="issuer-01")

# Verifies and decodes the CWT received from the presenter.
raw = cwt.decode(token, public_key)
decoded = Claims.new(raw)

# Extracts the PoP key from the CWT.
extracted_pop_key = COSEKey.new(decoded.cnf)  # = raw[8][1]

# Then, verifies the message sent by the presenter
# with the signature which is also sent by the presenter as follows:
extracted_pop_key.verify(msg, sig)

Usage Examples shows other examples which use other confirmation methods for PoP keys.

CWT with Private CA

Python CWT supports the case of using an arbitrary private CA as a root of trust. In this case, a COSE message sender needs to specify the trust relationship chaining up to the root CA by using x5chain header parameter. On the other hand, a COSE message receiver needs to specify trusted root CAs by using ca_certs parameter of CWT/COSE constructor (CWT.new() or COSE.new()).

import cwt
from cwt import Claims, COSEKey

# The sernder side:
with open("./private_key_of_cert.pem") as f:
    private_key = COSEKey.from_pem(f.read(), kid="01")

token = cwt.encode(
    {"iss": "coaps://as.example", "sub": "dajiaji", "cti": "123"}, private_key
)

# The recipient side:
public_key = COSEKey.from_jwk(
    {
        "kty": "EC",
        "use": "sig",
        "crv": "P-256",
        "kid": "P-256-01",
        "x": "oONCv1QoiajIbcW21Dqy6EnGvBTuF26GU7dy6JzOfXk",
        "y": "sl6k77K0TS36FW-TyEGLHY14ovZfdZ9DZWsbA8BTHGc",
        "x5c": [
            # The DER formatted X509 certificate which pairs with the private_key_of_cert.pem above.
            "MIIClDCCAXygAwIBAgIBBDANBgkqhkiG9w0BAQsFADBmMQswCQYDVQQGEwJKUDEOMAwGA1UECAwFVG9reW8xEDAOBgNVBAoMB2RhamlhamkxEzARBgNVBAMMCnB5dGhvbi1jd3QxIDAeBgkqhkiG9w0BCQEWEWRhamlhamlAZ21haWwuY29tMB4XDTIxMTAwMzEzMDE1MFoXDTMxMTAwMTEzMDE1MFowZDELMAkGA1UEBhMCSlAxDjAMBgNVBAgMBVRva3lvMQ0wCwYDVQQKDAR0ZXN0MRUwEwYDVQQDDAx0ZXN0LmV4YW1wbGUxHzAdBgkqhkiG9w0BCQEWEHRlc3RAZXhhbXBsZS5jb20wWTATBgcqhkjOPQIBBggqhkjOPQMBBwNCAASg40K_VCiJqMhtxbbUOrLoSca8FO4XboZTt3LonM59ebJepO-ytE0t-hVvk8hBix2NeKL2X3WfQ2VrGwPAUxxnoxowGDAJBgNVHRMEAjAAMAsGA1UdDwQEAwIE8DANBgkqhkiG9w0BAQsFAAOCAQEAZFfvFbaDk_DmG2cPGTwqwnFok1QnH2Tzkjk7p4vs1ycWzEDltkhyzcJxTSHoQGdykf7fG8NCrEqfi1G3hOyAtGxVIVcqsI-KIJCESp43zrNz5HsbwEY8l5rvcwohKGlE_idIFt5IuDTv7vsg_FaCIDeruw0NrXAACnLTwksawsxaCvtY12U0wsI2aC2Sb6V3HL-OLgcN6ZWzZ054L88JllckYnqJB8wCVBzzX2K2sZH3yeS39oRWZOVG6fwXsX4k0fHFx-Fn6KlrBU15pbjMLMn0ow0X3Y8e7FOgfkkph-N7e2SxceXNjrLiumOdclPm9yGSWoGsOJdId53dPvqAsQ",
            # The root certificate which is used for signing the above certificate (optional).
            "MIIDrzCCApegAwIBAgIUIK_CYzdq4BLLVXqSclNBgXy6mgswDQYJKoZIhvcNAQELBQAwZjELMAkGA1UEBhMCSlAxDjAMBgNVBAgMBVRva3lvMRAwDgYDVQQKDAdkYWppYWppMRMwEQYDVQQDDApweXRob24tY3d0MSAwHgYJKoZIhvcNAQkBFhFkYWppYWppQGdtYWlsLmNvbTAgFw0yMTEwMDIyMzU0NTZaGA8yMDcxMDkyMDIzNTQ1NlowZjELMAkGA1UEBhMCSlAxDjAMBgNVBAgMBVRva3lvMRAwDgYDVQQKDAdkYWppYWppMRMwEQYDVQQDDApweXRob24tY3d0MSAwHgYJKoZIhvcNAQkBFhFkYWppYWppQGdtYWlsLmNvbTCCASIwDQYJKoZIhvcNAQEBBQADggEPADCCAQoCggEBANFg4sw-uPWbPBbkJuohXc89O0gaqG1H2i1wzxxka32XNKIdwrxOJvsB2eALo3q7dTqLKCgzrjdd5N07gi0KzqjoIXIXqKpV5tm0fP5gCzEOWgxySCfBJOJyyvO6WvYXdvukEBnL-48D8RSjQH9fQEju5RG0taFZE-0nQ7n3P0J-Q-OfBUEoRiHvCd8oUx0s-fBpKdfhMAbD1sGAQ9CokUFeWc49em8inNqia5xljBtSYo6_2Zx9eb7B53wvBC0EmtS4SRyksR2emlr6GxMj_EZW7hcTfZCM4V2JYXliuAEdxA0sB7q-WqLg4OvltBQxCBgTTEXRCzxj3XXZy7QyUacCAwEAAaNTMFEwHQYDVR0OBBYEFA9id2cL_Chjv6liRN3HD849TARsMB8GA1UdIwQYMBaAFA9id2cL_Chjv6liRN3HD849TARsMA8GA1UdEwEB_wQFMAMBAf8wDQYJKoZIhvcNAQELBQADggEBAArIej5eJN1OmD3l3ef9QzosCxKThNwqNY55CoSSC3IRl-IAXy9Lvx7cgiliwBgCv99RbXZ1ZnptTHC_1kzMzPhPg9pGKDowFP-rywaB9-NTuHTWQ4hkKDsru5dpf75ILNI5PTUi1iiBM7TdgSerpEVroUWZiOpGAdlKkmE1h4gkR6eQY9Q0IvVXwagy_PPoQ1XO1i5Hyg3aXeDZBgkE7AuW9uxtYQHzg8JG2TNko_yp497yf_Ew4t6KzGDhSa8L1euMPtclALDWFhgl6WmYsHOqAOsyZOLwpsifWa533wI9mtTvLEg8TFKMOdU0sbAoQSbrrI9m4QS7mzDLchngj3E",
        ],
        "alg": "ES256",
    }
)

# The recipient can specify trusted CAs as follows:
decoder = CWT.new(ca_certs="/path/to/cacerts.pem")
decoded = decoder.decode(token, public_key)
assert 1 in decoded and decoded[1] == "coaps://as.example"

CWT for EUDCC (EU Digital COVID Certificate)

Python CWT supports Electronic Health Certificate Specification and EUDCC (EU Digital COVID Certificate) compliant with Technical Specifications for Digital Green Certificates Volume 1

A following example shows how to verify an EUDCC:

import cwt
from cwt import load_pem_hcert_dsc

# A DSC(Document Signing Certificate) issued by a CSCA
# (Certificate Signing Certificate Authority) quoted from:
# https://github.com/eu-digital-green-certificates/dgc-testdata/blob/main/AT/2DCode/raw/1.json
dsc = "-----BEGIN CERTIFICATE-----\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\n-----END CERTIFICATE-----"

# An EUDCC (EU Digital COVID Certificate) quoted from:
# https://github.com/eu-digital-green-certificates/dgc-testdata/blob/main/AT/2DCode/raw/1.json
eudcc = bytes.fromhex(
    "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"
)

public_key = load_pem_hcert_dsc(dsc)
decoded = cwt.decode(eudcc, keys=[public_key])
claims = Claims.new(decoded)
# claims.hcert[1] ==
# {
#     'v': [
#         {
#             'dn': 1,
#             'ma': 'ORG-100030215',
#             'vp': '1119349007',
#             'dt': '2021-02-18',
#             'co': 'AT',
#             'ci': 'URN:UVCI:01:AT:10807843F94AEE0EE5093FBC254BD813#B',
#             'mp': 'EU/1/20/1528',
#             'is': 'Ministry of Health, Austria',
#             'sd': 2,
#             'tg': '840539006',
#         }
#     ],
#     'nam': {
#         'fnt': 'MUSTERFRAU<GOESSINGER',
#         'fn': 'Musterfrau-Gößinger',
#         'gnt': 'GABRIELE',
#         'gn': 'Gabriele',
#     },
#     'ver': '1.0.0',
#     'dob': '1998-02-26',
# }

API Reference

See Documentation.

Supported CWT Claims

See Documentation.

Supported COSE Algorithms

See Documentation.

Referenced Specifications

Python CWT is (partially) compliant with following specifications:

• RFC9052: CBOR Object Signing and Encryption (COSE): Structures and Process
• RFC9053: CBOR Object Signing and Encryption (COSE): Initial Algorithms
• RFC9338: CBOR Object Signing and Encryption (COSE): Countersignatures - experimental
• RFC8812: COSE and JOSE Registrations for Web Authentication (WebAuthn) Algorithms
• RFC8747: Proof-of-Possession Key Semantics for CBOR Web Tokens (CWTs)
• RFC8392: CWT (CBOR Web Token)
• RFC8230: Using RSA Algorithms with COSE Messages
• RFC9459: CBOR Object Signing and Encryption (COSE): AES-CTR and AES-CBC - experimental
• RFC8152: CBOR Object Signing and Encryption (COSE)
• draft-07: Use of HPKE with COSE - experimental
• draft-06: CWT Claims in COSE Headers - experimental
• Electronic Health Certificate Specification
• Technical Specifications for Digital Green Certificates Volume 1

Tests

You can run tests from the project root after cloning with:

$ tox

Contributing

We welcome all kind of contributions, filing issues, suggesting new features or sending PRs.