The hash127mac library interface

unsigned int len ;
unsigned char const *key ;
H127MACSchedule ctx ;

 hash127mac_init(&ctx, key, len) ;

hash127mac_init() initializes the ctx H127MACSchedule structure with len bytes of secret read from key. The first 16 bytes are the hash127 secret ; the rest are used to initialize a RC4 generator. To be secure, the total secret length must be greater than 48. minssl uses 80-byte secrets.

H127MACSchedule ctx ;
int32 mac[4] ;
char const *message ;
unsigned int len ;

 hash127mac(&ctx, mac, message, len) ;

hash127mac() computes a secure authenticator for message of length len, and stores it into mac. Be careful: message must be aligned like an array of int32, and its length must be a multiple of 4. Pad it with zeros if you need.

hash127mac() uses a RC4-generated pseudorandom number as the hash127 k[n] secret, so the receiver side has to check the message authenticators in the same order as the sender side computes them. hash127mac is the ideal authenticator to use with a stream cipher, but its use is very limited otherwise.