vendor.github.com.pion.srtp.v2.crypto.go Maven / Gradle / Ivy
package srtp
import (
"crypto/cipher"
)
// xorBytes computes the exclusive-or of src1 and src2 and stores it in dst.
// It returns the number of bytes written.
func xorBytes(dst, src1, src2 []byte) int {
n := len(src1)
if len(src2) < n {
n = len(src2)
}
if len(dst) < n {
n = len(dst)
}
for i := 0; i < n; i++ {
dst[i] = src1[i] ^ src2[i]
}
return n
}
// incrementCTR increments a big-endian integer of arbitrary size.
func incrementCTR(ctr []byte) {
for i := len(ctr) - 1; i >= 0; i-- {
ctr[i]++
if ctr[i] != 0 {
break
}
}
}
// xorBytesCTR performs CTR encryption and decryption.
// It is equivalent to cipher.NewCTR followed by XORKeyStream.
func xorBytesCTR(block cipher.Block, iv []byte, dst, src []byte) error {
if len(iv) != block.BlockSize() {
return errBadIVLength
}
ctr := make([]byte, len(iv))
copy(ctr, iv)
bs := block.BlockSize()
stream := make([]byte, bs)
i := 0
for i < len(src) {
block.Encrypt(stream, ctr)
incrementCTR(ctr)
n := xorBytes(dst[i:], src[i:], stream)
if n == 0 {
break
}
i += n
}
return nil
}