/
sm4.go
47 lines (41 loc) · 941 Bytes
/
sm4.go
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package sm4bs
import (
"encoding/binary"
"math/bits"
)
// Key expansion algorithm.
func expandKey(key []byte, enc, dec []uint32) {
// Encryption key setup.
var i int
var mk []uint32
var k [rounds + 4]uint32
nk := len(key) / 4
mk = make([]uint32, nk)
for i = 0; i < nk; i++ {
mk[i] = binary.BigEndian.Uint32(key[4*i:])
k[i] = mk[i] ^ fk[i]
}
for i = 0; i < rounds; i++ {
k[i+4] = k[i] ^ t2(k[i+1]^k[i+2]^k[i+3]^ck[i])
enc[i] = k[i+4]
}
// Derive decryption key from encryption key.
if dec == nil {
return
}
for i = 0; i < rounds; i++ {
dec[i] = enc[rounds-1-i]
}
}
//L'(B)
func l2(b uint32) uint32 {
return b ^ bits.RotateLeft32(b, 13) ^ bits.RotateLeft32(b, 23)
}
func t2(in uint32) uint32 {
var bytes [4]byte
binary.BigEndian.PutUint32(bytes[:], in)
for i := 0; i < 4; i++ {
bytes[i] = sbox[bytes[i]]
}
return l2(binary.BigEndian.Uint32(bytes[:]))
}