Example #1
0
// Given the supplied cipher, whose block size must be 16 bytes, return two
// subkeys that can be used in MAC generation. See section 5.3 of NIST SP
// 800-38B. Note that the other NIST-approved block size of 8 bytes is not
// supported by this function.
func generateSubkeys(ciph cipher.Block) (k1 []byte, k2 []byte) {
	if ciph.BlockSize() != blockSize {
		panic("generateSubkeys requires a cipher with a block size of 16 bytes.")
	}

	// Step 1
	l := make([]byte, blockSize)
	ciph.Encrypt(l, subkeyZero)

	// Step 2: Derive the first subkey.
	if common.Msb(l) == 0 {
		// TODO(jacobsa): Accept a destination buffer in ShiftLeft and then hoist
		// the allocation in the else branch below.
		k1 = common.ShiftLeft(l)
	} else {
		k1 = make([]byte, blockSize)
		common.Xor(k1, common.ShiftLeft(l), subkeyRb)
	}

	// Step 3: Derive the second subkey.
	if common.Msb(k1) == 0 {
		k2 = common.ShiftLeft(k1)
	} else {
		k2 = make([]byte, blockSize)
		common.Xor(k2, common.ShiftLeft(k1), subkeyRb)
	}

	return
}
Example #2
0
func (t *ShiftLeftTest) MultiByteBuffers() {
	var input []byte
	var expected []byte

	input = []byte{fromBinary("00000000"), fromBinary("00000000")}
	expected = []byte{fromBinary("00000000"), fromBinary("00000000")}
	ExpectThat(common.ShiftLeft(input), DeepEquals(expected))

	input = []byte{fromBinary("00001000"), fromBinary("01000000")}
	expected = []byte{fromBinary("00010000"), fromBinary("10000000")}
	ExpectThat(common.ShiftLeft(input), DeepEquals(expected))

	input = []byte{fromBinary("10000000"), fromBinary("00000000")}
	expected = []byte{fromBinary("00000000"), fromBinary("00000000")}
	ExpectThat(common.ShiftLeft(input), DeepEquals(expected))

	input = []byte{fromBinary("01000001"), fromBinary("10000001")}
	expected = []byte{fromBinary("10000011"), fromBinary("00000010")}
	ExpectThat(common.ShiftLeft(input), DeepEquals(expected))
}
Example #3
0
// Given a 128-bit binary string, shift the string left by one bit and XOR the
// result with 0x00...87 if the bit shifted off was one. This is the dbl
// function of RFC 5297.
func dbl(b []byte) []byte {
	if len(b) != aes.BlockSize {
		panic("dbl requires a 16-byte buffer.")
	}

	shiftedOne := common.Msb(b) == 1
	b = common.ShiftLeft(b)
	if shiftedOne {
		tmp := make([]byte, aes.BlockSize)
		common.Xor(tmp, b, dblRb)
		b = tmp
	}

	return b
}
Example #4
0
func (t *ShiftLeftTest) EmptyBuffer() {
	f := func() { common.ShiftLeft([]byte{}) }
	ExpectThat(f, Panics(HasSubstr("empty")))
}
Example #5
0
func (t *ShiftLeftTest) NilBuffer() {
	f := func() { common.ShiftLeft(nil) }
	ExpectThat(f, Panics(HasSubstr("empty")))
}