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eea.go
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eea.go
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package zuc
// Just for reference, no performance advantage due to the block size / chunk are 4 bytes only!
import (
"crypto/cipher"
"encoding/binary"
"github.com/emmansun/gmsm/internal/subtle"
"github.com/emmansun/gmsm/internal/xor"
)
// NewCipher create a stream cipher based on key and iv aguments.
func NewCipher(key, iv []byte) (cipher.Stream, error) {
return newZUCState(key, iv)
}
// NewEEACipher create a stream cipher based on key, count, bearer and direction arguments according specification.
func NewEEACipher(key []byte, count, bearer, direction uint32) (cipher.Stream, error) {
iv := make([]byte, 16)
binary.BigEndian.PutUint32(iv, count)
copy(iv[8:12], iv[:4])
iv[4] = byte(((bearer << 1) | (direction & 1)) << 2)
iv[12] = iv[4]
return newZUCState(key, iv)
}
// Per test, even we generate key stream first, and then XOR once, the performance
// improvement is NOT significant.
func (c *zucState32) XORKeyStream(dst, src []byte) {
if len(dst) < len(src) {
panic("zuc: output smaller than input")
}
if subtle.InexactOverlap(dst[:len(src)], src) {
panic("zuc: invalid buffer overlap")
}
words := (len(src) + 3) / 4
var keyWords [4]byte
for i := 0; i < words; i++ {
binary.BigEndian.PutUint32(keyWords[:], c.genKeyword())
xor.XorBytes(dst, src, keyWords[:])
if i < words-1 {
dst = dst[4:]
src = src[4:]
}
}
}