diff options
Diffstat (limited to 'vendor/golang.org/x/crypto/chacha20/chacha_generic.go')
| -rw-r--r-- | vendor/golang.org/x/crypto/chacha20/chacha_generic.go | 119 |
1 files changed, 63 insertions, 56 deletions
diff --git a/vendor/golang.org/x/crypto/chacha20/chacha_generic.go b/vendor/golang.org/x/crypto/chacha20/chacha_generic.go index 7c498e90d..a2ecf5c32 100644 --- a/vendor/golang.org/x/crypto/chacha20/chacha_generic.go +++ b/vendor/golang.org/x/crypto/chacha20/chacha_generic.go @@ -42,10 +42,14 @@ type Cipher struct { // The last len bytes of buf are leftover key stream bytes from the previous // XORKeyStream invocation. The size of buf depends on how many blocks are - // computed at a time. + // computed at a time by xorKeyStreamBlocks. buf [bufSize]byte len int + // overflow is set when the counter overflowed, no more blocks can be + // generated, and the next XORKeyStream call should panic. + overflow bool + // The counter-independent results of the first round are cached after they // are computed the first time. precompDone bool @@ -89,6 +93,7 @@ func newUnauthenticatedCipher(c *Cipher, key, nonce []byte) (*Cipher, error) { return nil, errors.New("chacha20: wrong nonce size") } + key, nonce = key[:KeySize], nonce[:NonceSize] // bounds check elimination hint c.key = [8]uint32{ binary.LittleEndian.Uint32(key[0:4]), binary.LittleEndian.Uint32(key[4:8]), @@ -139,15 +144,18 @@ func quarterRound(a, b, c, d uint32) (uint32, uint32, uint32, uint32) { // SetCounter sets the Cipher counter. The next invocation of XORKeyStream will // behave as if (64 * counter) bytes had been encrypted so far. // -// To prevent accidental counter reuse, SetCounter panics if counter is -// less than the current value. +// To prevent accidental counter reuse, SetCounter panics if counter is less +// than the current value. +// +// Note that the execution time of XORKeyStream is not independent of the +// counter value. func (s *Cipher) SetCounter(counter uint32) { // Internally, s may buffer multiple blocks, which complicates this // implementation slightly. When checking whether the counter has rolled // back, we must use both s.counter and s.len to determine how many blocks // we have already output. outputCounter := s.counter - uint32(s.len)/blockSize - if counter < outputCounter { + if s.overflow || counter < outputCounter { panic("chacha20: SetCounter attempted to rollback counter") } @@ -196,34 +204,52 @@ func (s *Cipher) XORKeyStream(dst, src []byte) { dst[i] = src[i] ^ b } s.len -= len(keyStream) - src = src[len(keyStream):] - dst = dst[len(keyStream):] + dst, src = dst[len(keyStream):], src[len(keyStream):] + } + if len(src) == 0 { + return } - const blocksPerBuf = bufSize / blockSize - numBufs := (uint64(len(src)) + bufSize - 1) / bufSize - if uint64(s.counter)+numBufs*blocksPerBuf >= 1<<32 { + // If we'd need to let the counter overflow and keep generating output, + // panic immediately. If instead we'd only reach the last block, remember + // not to generate any more output after the buffer is drained. + numBlocks := (uint64(len(src)) + blockSize - 1) / blockSize + if s.overflow || uint64(s.counter)+numBlocks > 1<<32 { panic("chacha20: counter overflow") + } else if uint64(s.counter)+numBlocks == 1<<32 { + s.overflow = true } // xorKeyStreamBlocks implementations expect input lengths that are a // multiple of bufSize. Platform-specific ones process multiple blocks at a // time, so have bufSizes that are a multiple of blockSize. - rem := len(src) % bufSize - full := len(src) - rem - + full := len(src) - len(src)%bufSize if full > 0 { s.xorKeyStreamBlocks(dst[:full], src[:full]) } + dst, src = dst[full:], src[full:] + + // If using a multi-block xorKeyStreamBlocks would overflow, use the generic + // one that does one block at a time. + const blocksPerBuf = bufSize / blockSize + if uint64(s.counter)+blocksPerBuf > 1<<32 { + s.buf = [bufSize]byte{} + numBlocks := (len(src) + blockSize - 1) / blockSize + buf := s.buf[bufSize-numBlocks*blockSize:] + copy(buf, src) + s.xorKeyStreamBlocksGeneric(buf, buf) + s.len = len(buf) - copy(dst, buf) + return + } // If we have a partial (multi-)block, pad it for xorKeyStreamBlocks, and // keep the leftover keystream for the next XORKeyStream invocation. - if rem > 0 { + if len(src) > 0 { s.buf = [bufSize]byte{} - copy(s.buf[:], src[full:]) + copy(s.buf[:], src) s.xorKeyStreamBlocks(s.buf[:], s.buf[:]) - s.len = bufSize - copy(dst[full:], s.buf[:]) + s.len = bufSize - copy(dst, s.buf[:]) } } @@ -260,7 +286,9 @@ func (s *Cipher) xorKeyStreamBlocksGeneric(dst, src []byte) { s.precompDone = true } - for i := 0; i < len(src); i += blockSize { + // A condition of len(src) > 0 would be sufficient, but this also + // acts as a bounds check elimination hint. + for len(src) >= 64 && len(dst) >= 64 { // The remainder of the first column round. fcr0, fcr4, fcr8, fcr12 := quarterRound(c0, c4, c8, s.counter) @@ -285,49 +313,28 @@ func (s *Cipher) xorKeyStreamBlocksGeneric(dst, src []byte) { x3, x4, x9, x14 = quarterRound(x3, x4, x9, x14) } - // Finally, add back the initial state to generate the key stream. - x0 += c0 - x1 += c1 - x2 += c2 - x3 += c3 - x4 += c4 - x5 += c5 - x6 += c6 - x7 += c7 - x8 += c8 - x9 += c9 - x10 += c10 - x11 += c11 - x12 += s.counter - x13 += c13 - x14 += c14 - x15 += c15 + // Add back the initial state to generate the key stream, then + // XOR the key stream with the source and write out the result. + addXor(dst[0:4], src[0:4], x0, c0) + addXor(dst[4:8], src[4:8], x1, c1) + addXor(dst[8:12], src[8:12], x2, c2) + addXor(dst[12:16], src[12:16], x3, c3) + addXor(dst[16:20], src[16:20], x4, c4) + addXor(dst[20:24], src[20:24], x5, c5) + addXor(dst[24:28], src[24:28], x6, c6) + addXor(dst[28:32], src[28:32], x7, c7) + addXor(dst[32:36], src[32:36], x8, c8) + addXor(dst[36:40], src[36:40], x9, c9) + addXor(dst[40:44], src[40:44], x10, c10) + addXor(dst[44:48], src[44:48], x11, c11) + addXor(dst[48:52], src[48:52], x12, s.counter) + addXor(dst[52:56], src[52:56], x13, c13) + addXor(dst[56:60], src[56:60], x14, c14) + addXor(dst[60:64], src[60:64], x15, c15) s.counter += 1 - if s.counter == 0 { - panic("chacha20: internal error: counter overflow") - } - in, out := src[i:], dst[i:] - in, out = in[:blockSize], out[:blockSize] // bounds check elimination hint - - // XOR the key stream with the source and write out the result. - xor(out[0:], in[0:], x0) - xor(out[4:], in[4:], x1) - xor(out[8:], in[8:], x2) - xor(out[12:], in[12:], x3) - xor(out[16:], in[16:], x4) - xor(out[20:], in[20:], x5) - xor(out[24:], in[24:], x6) - xor(out[28:], in[28:], x7) - xor(out[32:], in[32:], x8) - xor(out[36:], in[36:], x9) - xor(out[40:], in[40:], x10) - xor(out[44:], in[44:], x11) - xor(out[48:], in[48:], x12) - xor(out[52:], in[52:], x13) - xor(out[56:], in[56:], x14) - xor(out[60:], in[60:], x15) + src, dst = src[blockSize:], dst[blockSize:] } } |