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pkg/cryptstate/ocb2: update times2 documentation.

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This commit is contained in:
Mikkel Krautz 2012-12-02 12:33:24 +01:00
parent 5c54c17247
commit 66c82c9a91
1 changed files with 13 additions and 0 deletions
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13
pkg/cryptstate/ocb2/ocb2.go
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@ -57,6 +57,19 @@ func xor(dst []byte, a []byte, b []byte) {
// irreducible polynomials [G. Seroussi, // irreducible polynomials [G. Seroussi,
// "Table of low-weight binary irreducible polynomials", // "Table of low-weight binary irreducible polynomials",
// HP Labs Technical Report HPL-98-135, 1998.]. // HP Labs Technical Report HPL-98-135, 1998.].
//
// and num2str(x, n) is defined as
//
// num2str(x, n)
// The n-bit binary representation of the integer x.
// More formally, the n-bit string S where x = S[1] *
// 2^{n-1} + S[2] * 2^{n-2} + ... + S[n] * 2^{0}. Only
// used when 0 <= x < 2^n.
//
// For our 128-bit block size implementation, this means that
// the xor with const(bitlength(S)) if S[1] = 1 is implemented
// by simply xor'ing the last byte with the number 135 when
// S[1] = 1.
func times2(block []byte) { func times2(block []byte) {
carry := (block[0] >> 7) & 0x1 carry := (block[0] >> 7) & 0x1
for i := 0; i < aes.BlockSize-1; i++ { for i := 0; i < aes.BlockSize-1; i++ {