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server/vendor/github.com/pion/srtp/v2/crypto.go

@@ -0,0 +1,45 @@
+// SPDX-FileCopyrightText: 2023 The Pion community <https://pion.ly>
+// SPDX-License-Identifier: MIT
+
+package srtp
+
+import (
+	"crypto/cipher"
+
+	"github.com/pion/transport/v2/utils/xor"
+)
+
+// 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 := xor.XorBytes(dst[i:], src[i:], stream)
+		if n == 0 {
+			break
+		}
+		i += n
+	}
+	return nil
+}