pysequoia 0.1.23

Provides OpenPGP facilities using Sequoia-PGP library

PySequoia

This library provides OpenPGP facilities in Python through the Sequoia PGP library. If you need to work with encryption and digital signatures using an IETF standardized protocol, this package is for you!

Note: This is a work in progress. The API is not stable!

Building

set -euxo pipefail
python -m venv .env
source .env/bin/activate
pip install maturin
maturin develop

Installing

PySequoia can be installed through pip:

pip install pysequoia

Note that since pysequoia is implemented largely in Rust, a Rust toolchain is necessary for the installation to succeed.

Testing

This entire document is used for end-to-end integration tests that exercise the package's API surface.

The tests assume that these keys and cards exist:

# generate a key with password
gpg --batch --pinentry-mode loopback --passphrase hunter22 --quick-gen-key [e-mail]
gpg --batch --pinentry-mode loopback --passphrase hunter22 --export-secret-key [e-mail] > passwd.pgp

# generate a key without password
gpg --batch --pinentry-mode loopback --passphrase '' --quick-gen-key [e-mail] future-default
gpg --batch --pinentry-mode loopback --passphrase '' --export-secret-key [e-mail] > no-passwd.pgp

# initialize dummy OpenPGP Card
sh /start.sh
echo 12345678 > pin
CARD_ADMIN="opgpcard admin --card 0000:00000000 --admin-pin pin"
$CARD_ADMIN import full-key.asc
$CARD_ADMIN name "John Doe"
$CARD_ADMIN url "https://example.com/key.pgp"
$CARD_ADMIN touch --key SIG --policy Fixed
$CARD_ADMIN touch --key DEC --policy Off
$CARD_ADMIN touch --key AUT --policy Fixed

Functions

All examples assume that these basic classes have been imported:

from pysequoia import Cert

sign

Signs data and returns armored output:

from pysequoia import sign

s = Cert.from_file("signing-key.asc")
signed = sign(s.secrets.signer(), "data to be signed".encode("utf8"))
print(f"Signed data: {signed}")
assert "PGP MESSAGE" in str(signed)

verify

Verifies signed data and returns verified data:

from pysequoia import verify

# sign some data
signing_key = Cert.from_file("signing-key.asc")
signed = sign(s.secrets.signer(), "data to be signed".encode("utf8"))

def get_certs(key_ids):
  # key_ids is an array of required signing keys
  print(f"For verification, we need these keys: {key_ids}")
  return [signing_key]

# verify the data
result = verify(signed, get_certs)
assert result.bytes.decode("utf8") == "data to be signed"

# let's check the valid signature's certificate and signing subkey fingerprints
assert result.valid_sigs[0].certificate == "afcf5405e8f49dbcd5dc548a86375b854b86acf9"
assert result.valid_sigs[0].signing_key == "afcf5405e8f49dbcd5dc548a86375b854b86acf9"

The function that returns certificates (here get_certs) may return more certificates than necessary.

verify succeeds if at least one correct signature has been made by any of the certificates supplied. If you need more advanced policies they can be implemented by inspecting the valid_sigs property.

encrypt

Signs and encrypts a string to one or more recipients:

from pysequoia import encrypt

s = Cert.from_file("passwd.pgp")
r = Cert.from_bytes(open("wiktor.asc", "rb").read())
bytes = "content to encrypt".encode("utf8")
encrypted = encrypt(signer = s.secrets.signer("hunter22"), recipients = [r], bytes = bytes).decode("utf8")
print(f"Encrypted data: {encrypted}")

The signer argument is optional and when omitted the function will return an unsigned (but encrypted) message.

decrypt

Decrypts plain data:

from pysequoia import decrypt

sender = Cert.from_file("no-passwd.pgp")
receiver = Cert.from_file("passwd.pgp")

content = "Red Green Blue"

encrypted = encrypt(recipients = [receiver], bytes = content.encode("utf8"))

decrypted = decrypt(decryptor = receiver.secrets.decryptor("hunter22"), bytes = encrypted)

assert content == decrypted.bytes.decode("utf8");

# this message did not contain any valid signatures
assert len(decrypted.valid_sigs) == 0

Decrypt can also verify signatures while decrypting:

from pysequoia import decrypt

sender = Cert.from_file("no-passwd.pgp")
receiver = Cert.from_file("passwd.pgp")

content = "Red Green Blue"

encrypted = encrypt(signer = sender.secrets.signer(), recipients = [receiver], bytes = content.encode("utf8"))

def get_certs(key_ids):
  print(f"For verification after decryption, we need these keys: {key_ids}")
  return [sender]

decrypted = decrypt(decryptor = receiver.secrets.decryptor("hunter22"), bytes = encrypted, store = get_certs)

assert content == decrypted.bytes.decode("utf8");

# let's check the valid signature's certificate and signing subkey fingerprints
assert decrypted.valid_sigs[0].certificate == sender.fingerprint
assert decrypted.valid_sigs[0].signing_key == sender.fingerprint

Here, the same remarks as to verify also apply.

Certificates

The Cert class represents one OpenPGP certificate (commonly called a "public key").

This package additionally verifies the certificate using Sequoia PGP's StandardPolicy. This means that certificates using weak cryptography can fail to load, or present a different view than in other OpenPGP software (e.g. if a User ID uses SHA-1 in its back-signature, it may be missing from the list of User IDs returned by this package).

Certificates have two forms, one is ASCII armored and one is raw bytes:

cert = Cert.generate("Test <[e-mail]>")

print(f"Armored cert: {cert}")
print(f"Bytes of the cert: {cert.bytes()}")

Parsing

Certificates can be parsed from files (Cert.from_file) or bytes in memory (Cert.from_bytes).

cert1 = Cert.generate("Test <[e-mail]>")
buffer = cert1.bytes()

parsed_cert = Cert.from_bytes(buffer)
assert str(parsed_cert.user_ids[0]) == "Test <[e-mail]>"

They can also be picked from "keyring" files (Cert.split_file) or bytes in memory (Cert.split_bytes) which are collections of binary certificates.

cert1 = Cert.generate("Test 1 <[e-mail]>")
cert2 = Cert.generate("Test 2 <[e-mail]>")
cert3 = Cert.generate("Test 3 <[e-mail]>")

buffer = cert1.bytes() + cert2.bytes() + cert3.bytes()
certs = Cert.split_bytes(buffer)
assert len(certs) == 3

generate

Creates a new general purpose key with a given User ID:

alice = Cert.generate("Alice <[e-mail]>")
fpr = alice.fingerprint
print(f"Generated cert with fingerprint {fpr}:\n{alice}")

Multiple User IDs can be passed as a list to the generate function:

cert = Cert.generate(user_ids = ["First", "Second", "Third"])
assert len(cert.user_ids) == 3

Newly generated certificates are usable in both encryption and signing contexts:

alice = Cert.generate("Alice <[e-mail]>")
bob = Cert.generate("Bob <[e-mail]>")

bytes = "content to encrypt".encode("utf8")

encrypted = encrypt(signer = alice.secrets.signer(), recipients = [bob], bytes = bytes)
print(f"Encrypted data: {encrypted}")

merge

Merges packets from a new version into an old version of a certificate:

old = Cert.from_file("wiktor.asc")
new = Cert.from_file("wiktor-fresh.asc")
merged = old.merge(new)

User IDs

Listing existing User IDs:

cert = Cert.from_file("wiktor.asc")
user_id = cert.user_ids[0]
assert str(user_id).startswith("Wiktor Kwapisiewicz")

Adding new User IDs:

cert = Cert.generate("Alice <[e-mail]>")
assert len(cert.user_ids) == 1;

cert = cert.add_user_id(value = "Alice <[e-mail]>", certifier = cert.secrets.certifier())

assert len(cert.user_ids) == 2;

Revoking User IDs:

cert = Cert.generate("Bob <[e-mail]>")

cert = cert.add_user_id(value = "Bob <[e-mail]>", certifier = cert.secrets.certifier())
assert len(cert.user_ids) == 2

# create User ID revocation
revocation = cert.revoke_user_id(user_id = cert.user_ids[1], certifier = cert.secrets.certifier())

# merge the revocation with the cert
cert = Cert.from_bytes(cert.bytes() + revocation.bytes())
assert len(cert.user_ids) == 1

Notations

Notations are small pieces of data that can be attached to signatures (and, indirectly, to User IDs).

The following example reads and displays a Keyoxide proof URI:

cert = Cert.from_file("wiktor.asc")
user_id = cert.user_ids[0]
notation = user_id.notations[0]

assert notation.key == "[e-mail]";
assert notation.value == "dns:metacode.biz?type=TXT";

Notations can also be added:

from pysequoia import Notation

cert = Cert.from_file("signing-key.asc")

# No notations initially
assert len(cert.user_ids[0].notations) == 0;

cert = cert.set_notations(cert.secrets.certifier(), [Notation("[e-mail]", "dns:metacode.biz")])

# Has one notation now
print(str(cert.user_ids[0].notations))
assert len(cert.user_ids[0].notations) == 1;

# Check the notation data
notation = cert.user_ids[0].notations[0]

assert notation.key == "[e-mail]";
assert notation.value == "dns:metacode.biz";

Key expiration

Certs have an expiration getter for retrieving the current key expiry time:

cert = Cert.from_file("signing-key.asc")

# Cert does not have any expiration date:
assert cert.expiration is None

cert = Cert.from_file("wiktor.asc")
# Cert expires on New Year's Eve
assert str(cert.expiration) == "2022-12-31 12:00:02+00:00"

Key expiration can also be adjusted with set_expiration:

from datetime import datetime

cert = Cert.from_file("signing-key.asc")

# Cert does not have any expiration date:
assert cert.expiration is None

# Set the expiration to some specified point in time
expiration = datetime.fromisoformat("2021-11-04T00:05:23+00:00")
cert = cert.set_expiration(expiration = expiration, certifier = cert.secrets.certifier())
assert str(cert.expiration) == "2021-11-04 00:05:23+00:00"

Key revocation

Certs can be revoked. While expiration makes the key unusable temporarily to encourage the user to refresh a copy revocation is irreversible.

cert = Cert.generate("Test Revocation <[e-mail]>")
revocation = cert.revoke(certifier = cert.secrets.certifier())

# creating revocation signature does not revoke the key
assert not cert.is_revoked

# importing revocation signature marks the key as revoked
revoked_cert = Cert.from_bytes(cert.bytes() + revocation.bytes())
assert revoked_cert.is_revoked

Secret keys

Certificates generated through Cert.generate() contain secret keys and can be used for signing and decryption.

To avoid accidental leakage secret keys are never directly printed when the Cert is written to a string. To enable this behavior use Cert.secrets. secrets returns None on certificates which do not contain any secret key material ("public keys").

c = Cert.generate("Testing key <[e-mail]>")
assert c.has_secret_keys

# by default only public parts are exported
public_parts = Cert.from_bytes(f"{c}".encode("utf8"))
assert not public_parts.has_secret_keys
assert public_parts.secrets is None

# to export secret parts use the following:
private_parts = Cert.from_bytes(f"{c.secrets}".encode("utf8"))
assert private_parts.has_secret_keys

OpenPGP Cards

There's an experimental feature allowing communication with OpenPGP Cards (like YubiKey or Nitrokey).

from pysequoia import Card

# enumerate all cards
all = Card.all()

# open card by card ident
card = Card.open("0000:00000000")

print(f"Card ident: {card.ident}")
assert card.cardholder == "John Doe"
assert card.cert_url == "https://example.com/key.pgp"

Cards provide keys property that can be used to see which keys are imported on the card:

keys = card.keys
print(f"Keys: {keys}")
assert len(keys) == 3

assert keys[0].fingerprint == "ddc3e03c91fb52ca2d95c2444566f2743ed5f382"
assert "sign" in keys[0].usage
assert keys[0].touch_required

assert keys[1].fingerprint == "689e152a7420be13dcaf2c142ac27adc1db9395e"
assert "decrypt" in keys[1].usage
assert not keys[1].touch_required

assert keys[2].fingerprint == "731fbca93ce9821347bf8e696444723371d3c650"
assert "authenticate" in keys[2].usage
assert keys[2].touch_required

Cards can be used for signing data:

signer = card.signer("123456")

signed = sign(signer, "data to be signed".encode("utf8"))
print(f"Signed data: {signed}")

As well as for decryption:

decryptor = card.decryptor("123456")

sender = Cert.from_file("passwd.pgp")
receiver = Cert.from_file("full-key.asc")

content = "Red Green Blue"

encrypted = encrypt(signer = sender.secrets.signer("hunter22"), recipients = [receiver], bytes = content.encode("utf8"))

print(f"Encrypted data: {encrypted}")

decrypted = decrypt(decryptor = decryptor, bytes = encrypted)

assert content == decrypted.bytes.decode("utf8");

Note that while this package allows using cards for signing and decryption, the provisioning process is not supported. OpenPGP card tools can be used to initialize the card.

License

This project is licensed under Apache License, Version 2.0.

Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the package by you shall be under the terms and conditions of this license, without any additional terms or conditions.

Sponsors

My work was supported by these generous organizations (alphabetical order):

• nlnet.nl
• pep.foundation
• sovereigntechfund.de