[Cryptography] Keccak-based AEAD cipher algorithm

[Stephan Mueller]

Hi,

Using Keccak, a symmetric stream cipher algorithm using the authenticated 
encryption with additional data (AEAD) algorithm can be specified.

I have developed such an AEAD algorithm implementation. This algorithm can be 
used to encrypt and decrypt arbitrary user data. The cipher algorithm uses the 
SP800-185 cSHAKE algorithm to generate a key stream which is XORed with either 
the plaintext (encryption) or ciphertext (decryption) data. The cSHAKE is 
initialized with the user-provided key and the user-provided IV. In addition, 
a second cSHAKE instance is initialized which calculates a keyed-message 
digest of the ciphertext to create a message authentication tag. This message 
authentication tag is used during decryption to verify the integrity of the 
ciphertext.

In addition, a very similar SP800-185 KMAC-based AEAD algorithm is also 
implemented.

The amount of code required to implement the respective algorithm is very 
limited.

Both AEAD stream cipher algorithms are fully documented and specified in [1] 
and [2] which also provide a working copy. The documentation in [1] also 
provides a comparison between both algorithms.

The API documentation of both algorithm implementations is given in [3] and 
[4].

I would be happy to receive comments or suggestions.

[1] https://github.com/smuellerDD/leancrypto/blob/master/aead/src/
cshake_crypt.c

[2] https://github.com/smuellerDD/leancrypto/blob/master/aead/src/kmac_crypt.c

[3] https://github.com/smuellerDD/leancrypto/blob/master/aead/api/
lc_cshake_crypt.h

[4] https://github.com/smuellerDD/leancrypto/blob/master/aead/api/
lc_kmac_crypt.h

Ciao
Stephan