46 lines
903 B
Go
46 lines
903 B
Go
// SPDX-FileCopyrightText: 2023 The Pion community <https://pion.ly>
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// SPDX-License-Identifier: MIT
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package srtp
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import (
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"crypto/cipher"
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"github.com/pion/transport/v2/utils/xor"
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)
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// incrementCTR increments a big-endian integer of arbitrary size.
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func incrementCTR(ctr []byte) {
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for i := len(ctr) - 1; i >= 0; i-- {
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ctr[i]++
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if ctr[i] != 0 {
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break
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}
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}
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}
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// xorBytesCTR performs CTR encryption and decryption.
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// It is equivalent to cipher.NewCTR followed by XORKeyStream.
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func xorBytesCTR(block cipher.Block, iv []byte, dst, src []byte) error {
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if len(iv) != block.BlockSize() {
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return errBadIVLength
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}
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ctr := make([]byte, len(iv))
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copy(ctr, iv)
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bs := block.BlockSize()
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stream := make([]byte, bs)
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i := 0
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for i < len(src) {
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block.Encrypt(stream, ctr)
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incrementCTR(ctr)
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n := xor.XorBytes(dst[i:], src[i:], stream)
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if n == 0 {
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break
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}
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i += n
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}
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return nil
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}
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