Keyed Streebog is a secure PRF and MAC

One of the most popular ways to turn a keyless hash function into a keyed one is the HMAC algorithm. This approach is too expensive in some cases due to double hashing. Excessive overhead can be avoided by using features of the hash function. The paper presents a simple and safe keyed cryptoalgorithm (conventionally called «Streebog-K») from hash function Streebog $\mathsf{H}(M)$. Let $K$ be a secret key, then $\mathsf{KH}(K,M)=\mathsf{H}(K||M)$ is a secure pseudorandom function (PRF) and, therefore, a good message authentification code (MAC). The proof is obtained by reduction of the security of the presented construction to the resistance of the underlying compression function to the related key attacks (PRF-RKA). The security bounds of Streebog-K are essentially the same as those of HMAC-Streebog, but the computing speed doubles when short messages are used.