incCounter increments a four byte, big-endian counter. func incCounter(c *[4]byte) { if c[3]++; c[3] != 0 { return } if c[2]++; c[2] != 0 { return } if c[1]++; c[1] != 0 { return } c[0]++ } // mgf1XOR XORs the bytes in out with a mask generated using the MGF1 function // specified in PKCS #1 v2.1. func mgf1XOR(out []byte, hash fips140.Hash, seed []byte) { var counter [4]byte var digest []byte done := 0 for done < len(out) { hash.Reset() hash.Write(seed) hash.Write(counter[0:4]) digest = hash.Sum(digest[:0])...