• Joy Latten's avatar
    [CRYPTO] ctr: Add CTR (Counter) block cipher mode · 23e353c8
    Joy Latten authored
    This patch implements CTR mode for IPsec.
    It is based off of RFC 3686.
    
    Please note:
    1. CTR turns a block cipher into a stream cipher.
    Encryption is done in blocks, however the last block
    may be a partial block.
    
    A "counter block" is encrypted, creating a keystream
    that is xor'ed with the plaintext. The counter portion
    of the counter block is incremented after each block
    of plaintext is encrypted.
    Decryption is performed in same manner.
    
    2. The CTR counterblock is composed of,
            nonce + IV + counter
    
    The size of the counterblock is equivalent to the
    blocksize of the cipher.
            sizeof(nonce) + sizeof(IV) + sizeof(counter) = blocksize
    
    The CTR template requires the name of the cipher
    algorithm, the sizeof the nonce, and the sizeof the iv.
            ctr(cipher,sizeof_nonce,sizeof_iv)
    
    So for example,
            ctr(aes,4,8)
    specifies the counterblock will be composed of 4 bytes
    from a nonce, 8 bytes from the iv, and 4 bytes for counter
    since aes has a blocksize of 16 bytes.
    
    3. The counter portion of the counter block is stored
    in big endian for conformance to rfc 3686.
    Signed-off-by: default avatarJoy Latten <latten@austin.ibm.com>
    Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
    23e353c8
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