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A Python implementation of Cocks' identity-based encryption (IBE) scheme.

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A Python implementation of Cocks' identity-based encryption (IBE) scheme [1]. IBE allows strings to be used directly as public encryption keys.

Cocks' scheme uses the quadratic residuosity hardness problem, rather than bilinear pairings with other IBE schemes, e.g. Boneh-Franklin [2]. As a result, no additional dependencies are required for pairing-based cryptography; only gmpy2 is sufficient.


Two classes are utilised for server- (PKG) and client-side communication:

  1. PKGCocksPKG: implements the public key generator (PKG) for the scheme's initialisation and extracting secret keys from identity strings.

  2. ClientCocks: used for encrypting and decrypting messages using the secret key and public modulus generated by CocksPKG.


from pycocks.cocks import CocksPKG

# Instantiate the PKG
# Optional parameters: bit size (default = 2048) and hash function (default = SHA512)
cocks_pkg = CocksPKG()   

# Extract private key, r, from an identity string. This is
# "User1" in this instance.
# A transformed ID string, a, is also returned that is
# required for encryption and decryption by the client.
r, a = cocks_pkg.extract("User1")


from pycocks.cocks import Cocks

# Instantiate the client
# Must use the same modulus, n, as the PKG
cocks = Cocks(cocks_pkg.n)  

# Encryption example
# Transformed identity string, a, is provided by the server PKG
c = cocks.encrypt(b"test", a)

# Decryption example
# Private key, r, is generated by the server PKG
msg = cocks.decrypt(c, r, a)  # => b"test"


Use pytest to execute tests in tests/


  • gmpy2 (tested v2.0.8)


Please use the following if you use pycocks in a publication:

      author={Carlton Shepherd},


  1. C. Cocks, "An identity based encryption scheme based on quadratic residues", Proceedings of the IMA International Conference on Cryptography and Coding. Springer, 2001.
  2. D. Boneh and M. Franklin, "Identity-based encryption from the Weil pairing", Annual International Cryptology Conference. Springer, 2001.

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