forked from External/grumble
pkg/cryptstate/ocb2: stricter cipher/tag/nonce checking.
This commit is contained in:
Mikkel Krautz
parent
66c82c9a91
commit
389e2f844d
1 changed files with 69 additions and 37 deletions
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@ -1,7 +1,9 @@
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// Package ocb2 implements the version 2 of the OCB authenticated-encryption algorithm.
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// OCB2 is specified in http://www.cs.ucdavis.edu/~rogaway/papers/draft-krovetz-ocb-00.txt.
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//
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// It should be noted that OCB's author, Phil Rogaway <rogaway@cs.ucdavis.edu>, holds
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// Note that this implementation is limited to block ciphers with a block size of 128 bits.
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//
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// It should also be noted that OCB's author, Phil Rogaway <rogaway@cs.ucdavis.edu>, holds
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// several US patents on the algorithm. This should be considered before using this code
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// in your own projects. See OCB's FAQ for more info:
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// http://www.cs.ucdavis.edu/~rogaway/ocb/ocb-faq.htm#patent:phil
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@ -10,19 +12,19 @@
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// free basis.
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package ocb2
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import (
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"crypto/aes"
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"crypto/cipher"
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)
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import "crypto/cipher"
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const (
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// BlockSize defines the block size that this particular implementation
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// of OCB2 is made to work on.
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BlockSize = 16
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// TagSize specifies the length in bytes of a full OCB2 tag.
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// As per the specification, applications may truncate their
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// tags to a given length, but advocates that typical applications
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// should use a tag length of at least 8 bytes (64 bits).
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TagSize = aes.BlockSize
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TagSize = BlockSize
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// NonceSize specifies the length in bytes of an OCB2 nonce.
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NonceSize = aes.BlockSize
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NonceSize = BlockSize
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)
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// zeros fills block with zero bytes.
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@ -34,7 +36,7 @@ func zeros(block []byte) {
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// xor outputs the bitwise exclusive-or of a and b to dst.
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func xor(dst []byte, a []byte, b []byte) {
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for i := 0; i < aes.BlockSize; i++ {
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for i := 0; i < BlockSize; i++ {
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dst[i] = a[i] ^ b[i]
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}
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}
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@ -72,10 +74,10 @@ func xor(dst []byte, a []byte, b []byte) {
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// S[1] = 1.
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func times2(block []byte) {
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carry := (block[0] >> 7) & 0x1
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for i := 0; i < aes.BlockSize-1; i++ {
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for i := 0; i < BlockSize-1; i++ {
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block[i] = (block[i] << 1) | ((block[i+1] >> 7) & 0x1)
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}
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block[aes.BlockSize-1] = (block[aes.BlockSize-1] << 1) ^ (carry * 135)
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block[BlockSize-1] = (block[BlockSize-1] << 1) ^ (carry * 135)
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}
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// times3 performs the times3 operation, defined as:
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@ -84,10 +86,10 @@ func times2(block []byte) {
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// times2(S) xor S
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func times3(block []byte) {
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carry := (block[0] >> 7) & 0x1
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for i := 0; i < aes.BlockSize-1; i++ {
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for i := 0; i < BlockSize-1; i++ {
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block[i] ^= (block[i] << 1) | ((block[i+1] >> 7) & 0x1)
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}
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block[aes.BlockSize-1] ^= ((block[aes.BlockSize-1] << 1) ^ (carry * 135))
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block[BlockSize-1] ^= ((block[BlockSize-1] << 1) ^ (carry * 135))
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}
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// Encrypt encrypts the plaintext src and outputs the corresponding ciphertext into dst.
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@ -98,39 +100,54 @@ func times3(block []byte) {
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// To ensure both authenticity and secrecy of messages, each invocation to this function must
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// be given an unique nonce of ocb2.NonceSize bytes. The nonce need not be secret (it can be
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// a counter), but it needs to be unique.
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//
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// The block cipher used in function must work on a block size equal to ocb2.BlockSize.
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// The tag slice used in this function must have a length equal to ocb2.TagSize.
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// The nonce slice used in this function must have a length equal to ocb2.NonceSize.
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// If any of the above are violated, Encrypt will panic.
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func Encrypt(cipher cipher.Block, dst []byte, src []byte, nonce []byte, tag []byte) {
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var delta [aes.BlockSize]byte
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var checksum [aes.BlockSize]byte
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var tmp [aes.BlockSize]byte
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var pad [aes.BlockSize]byte
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if cipher.BlockSize() != BlockSize {
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panic("ocb2: cipher blocksize is not equal to ocb2.BlockSize")
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}
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if len(nonce) != NonceSize {
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panic("ocb2: nonce length is not equal to ocb2.NonceSize")
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}
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if len(tag) != TagSize {
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panic("ocb2: tag length is not equal to ocb2.TagSize")
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}
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var delta [BlockSize]byte
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var checksum [BlockSize]byte
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var tmp [BlockSize]byte
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var pad [BlockSize]byte
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off := 0
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cipher.Encrypt(delta[0:], nonce[0:])
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zeros(checksum[0:])
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remain := len(src)
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for remain > aes.BlockSize {
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for remain > BlockSize {
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times2(delta[0:])
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xor(tmp[0:], delta[0:], src[off:off+aes.BlockSize])
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xor(tmp[0:], delta[0:], src[off:off+BlockSize])
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cipher.Encrypt(tmp[0:], tmp[0:])
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xor(dst[off:off+aes.BlockSize], delta[0:], tmp[0:])
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xor(checksum[0:], checksum[0:], src[off:off+aes.BlockSize])
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remain -= aes.BlockSize
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off += aes.BlockSize
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xor(dst[off:off+BlockSize], delta[0:], tmp[0:])
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xor(checksum[0:], checksum[0:], src[off:off+BlockSize])
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remain -= BlockSize
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off += BlockSize
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}
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times2(delta[0:])
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zeros(tmp[0:])
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num := remain * 8
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tmp[aes.BlockSize-2] = uint8((uint32(num) >> 8) & 0xff)
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tmp[aes.BlockSize-1] = uint8(num & 0xff)
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tmp[BlockSize-2] = uint8((uint32(num) >> 8) & 0xff)
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tmp[BlockSize-1] = uint8(num & 0xff)
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xor(tmp[0:], tmp[0:], delta[0:])
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cipher.Encrypt(pad[0:], tmp[0:])
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copied := copy(tmp[0:], src[off:])
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if copied != remain {
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panic("ocb2: copy failed")
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}
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if copy(tmp[copied:], pad[copied:]) != (aes.BlockSize - remain) {
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if copy(tmp[copied:], pad[copied:]) != (BlockSize - remain) {
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panic("ocb2: copy failed")
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}
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xor(checksum[0:], checksum[0:], tmp[0:])
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@ -151,32 +168,47 @@ func Encrypt(cipher cipher.Block, dst []byte, src []byte, nonce []byte, tag []by
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// should verify that the computed authentication tag matches the tag that was produced when
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// encrypting the message (taking into consideration that OCB tags are allowed to be truncated
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// to a length less than ocb.TagSize).
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//
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// The block cipher used in function must work on a block size equal to ocb2.BlockSize.
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// The tag slice used in this function must have a length equal to ocb2.TagSize.
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// The nonce slice used in this function must have a length equal to ocb2.NonceSize.
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// If any of the above are violated, Encrypt will panic.
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func Decrypt(cipher cipher.Block, plain []byte, encrypted []byte, nonce []byte, tag []byte) {
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var checksum [aes.BlockSize]byte
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var delta [aes.BlockSize]byte
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var tmp [aes.BlockSize]byte
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var pad [aes.BlockSize]byte
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if cipher.BlockSize() != BlockSize {
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panic("ocb2: cipher blocksize is not equal to ocb2.BlockSize")
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}
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if len(nonce) != NonceSize {
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panic("ocb2: nonce length is not equal to ocb2.NonceSize")
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}
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if len(tag) != TagSize {
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panic("ocb2: tag length is not equal to ocb2.TagSize")
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}
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var checksum [BlockSize]byte
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var delta [BlockSize]byte
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var tmp [BlockSize]byte
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var pad [BlockSize]byte
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off := 0
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cipher.Encrypt(delta[0:], nonce[0:])
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zeros(checksum[0:])
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remain := len(encrypted)
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for remain > aes.BlockSize {
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for remain > BlockSize {
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times2(delta[0:])
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xor(tmp[0:], delta[0:], encrypted[off:off+aes.BlockSize])
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xor(tmp[0:], delta[0:], encrypted[off:off+BlockSize])
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cipher.Decrypt(tmp[0:], tmp[0:])
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xor(plain[off:off+aes.BlockSize], delta[0:], tmp[0:])
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xor(checksum[0:], checksum[0:], plain[off:off+aes.BlockSize])
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off += aes.BlockSize
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remain -= aes.BlockSize
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xor(plain[off:off+BlockSize], delta[0:], tmp[0:])
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xor(checksum[0:], checksum[0:], plain[off:off+BlockSize])
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off += BlockSize
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remain -= BlockSize
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}
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times2(delta[0:])
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zeros(tmp[0:])
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num := remain * 8
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tmp[aes.BlockSize-2] = uint8((uint32(num) >> 8) & 0xff)
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tmp[aes.BlockSize-1] = uint8(num & 0xff)
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tmp[BlockSize-2] = uint8((uint32(num) >> 8) & 0xff)
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tmp[BlockSize-1] = uint8(num & 0xff)
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xor(tmp[0:], tmp[0:], delta[0:])
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cipher.Encrypt(pad[0:], tmp[0:])
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zeros(tmp[0:])
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