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// Copyright 2019 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
//go:build ppc64le
package aes
import (
"crypto/cipher"
"crypto/subtle"
"encoding/binary"
"errors"
)
// This file implements GCM using an optimized GHASH function.
//go:noescape
func gcmInit(productTable *[256]byte, h []byte)
//go:noescape
func gcmHash(output []byte, productTable *[256]byte, inp []byte, len int)
//go:noescape
func gcmMul(output []byte, productTable *[256]byte)
const (
gcmCounterSize = 16
gcmBlockSize = 16
gcmTagSize = 16
gcmStandardNonceSize = 12
)
var errOpen = errors.New("cipher: message authentication failed")
// Assert that aesCipherGCM implements the gcmAble interface.
var _ gcmAble = (*aesCipherAsm)(nil)
type gcmAsm struct {
cipher *aesCipherAsm
// ks is the key schedule, the length of which depends on the size of
// the AES key.
ks []uint32
// productTable contains pre-computed multiples of the binary-field
// element used in GHASH.
productTable [256]byte
// nonceSize contains the expected size of the nonce, in bytes.
nonceSize int
// tagSize contains the size of the tag, in bytes.
tagSize int
}
// NewGCM returns the AES cipher wrapped in Galois Counter Mode. This is only
// called by crypto/cipher.NewGCM via the gcmAble interface.
func (c *aesCipherAsm) NewGCM(nonceSize, tagSize int) (cipher.AEAD, error) {
g := &gcmAsm{cipher: c, ks: c.enc, nonceSize: nonceSize, tagSize: tagSize}
hle := make([]byte, gcmBlockSize)
c.Encrypt(hle, hle)
// Reverse the bytes in each 8 byte chunk
// Load little endian, store big endian
h1 := binary.LittleEndian.Uint64(hle[:8])
h2 := binary.LittleEndian.Uint64(hle[8:])
binary.BigEndian.PutUint64(hle[:8], h1)
binary.BigEndian.PutUint64(hle[8:], h2)
gcmInit(&g.productTable, hle)
return g, nil
}
func (g *gcmAsm) NonceSize() int {
return g.nonceSize
}
func (g *gcmAsm) Overhead() int {
return g.tagSize
}
func sliceForAppend(in []byte, n int) (head, tail []byte) {
if total := len(in) + n; cap(in) >= total {
head = in[:total]
} else {
head = make([]byte, total)
copy(head, in)
}
tail = head[len(in):]
return
}
// deriveCounter computes the initial GCM counter state from the given nonce.
func (g *gcmAsm) deriveCounter(counter *[gcmBlockSize]byte, nonce []byte) {
if len(nonce) == gcmStandardNonceSize {
copy(counter[:], nonce)
counter[gcmBlockSize-1] = 1
} else {
var hash [16]byte
g.paddedGHASH(&hash, nonce)
lens := gcmLengths(0, uint64(len(nonce))*8)
g.paddedGHASH(&hash, lens[:])
copy(counter[:], hash[:])
}
}
// counterCrypt encrypts in using AES in counter mode and places the result
// into out. counter is the initial count value and will be updated with the next
// count value. The length of out must be greater than or equal to the length
// of in.
func (g *gcmAsm) counterCrypt(out, in []byte, counter *[gcmBlockSize]byte) {
var mask [gcmBlockSize]byte
for len(in) >= gcmBlockSize {
// Hint to avoid bounds check
_, _ = in[15], out[15]
g.cipher.Encrypt(mask[:], counter[:])
gcmInc32(counter)
// XOR 16 bytes each loop iteration in 8 byte chunks
in0 := binary.LittleEndian.Uint64(in[0:])
in1 := binary.LittleEndian.Uint64(in[8:])
m0 := binary.LittleEndian.Uint64(mask[:8])
m1 := binary.LittleEndian.Uint64(mask[8:])
binary.LittleEndian.PutUint64(out[:8], in0^m0)
binary.LittleEndian.PutUint64(out[8:], in1^m1)
out = out[16:]
in = in[16:]
}
if len(in) > 0 {
g.cipher.Encrypt(mask[:], counter[:])
gcmInc32(counter)
// XOR leftover bytes
for i, inb := range in {
out[i] = inb ^ mask[i]
}
}
}
// increments the rightmost 32-bits of the count value by 1.
func gcmInc32(counterBlock *[16]byte) {
c := counterBlock[len(counterBlock)-4:]
x := binary.BigEndian.Uint32(c) + 1
binary.BigEndian.PutUint32(c, x)
}
// paddedGHASH pads data with zeroes until its length is a multiple of
// 16-bytes. It then calculates a new value for hash using the ghash
// algorithm.
func (g *gcmAsm) paddedGHASH(hash *[16]byte, data []byte) {
if siz := len(data) - (len(data) % gcmBlockSize); siz > 0 {
gcmHash(hash[:], &g.productTable, data[:], siz)
data = data[siz:]
}
if len(data) > 0 {
var s [16]byte
copy(s[:], data)
gcmHash(hash[:], &g.productTable, s[:], len(s))
}
}
// auth calculates GHASH(ciphertext, additionalData), masks the result with
// tagMask and writes the result to out.
func (g *gcmAsm) auth(out, ciphertext, aad []byte, tagMask *[gcmTagSize]byte) {
var hash [16]byte
g.paddedGHASH(&hash, aad)
g.paddedGHASH(&hash, ciphertext)
lens := gcmLengths(uint64(len(aad))*8, uint64(len(ciphertext))*8)
g.paddedGHASH(&hash, lens[:])
copy(out, hash[:])
for i := range out {
out[i] ^= tagMask[i]
}
}
// Seal encrypts and authenticates plaintext. See the cipher.AEAD interface for
// details.
func (g *gcmAsm) Seal(dst, nonce, plaintext, data []byte) []byte {
if len(nonce) != g.nonceSize {
panic("cipher: incorrect nonce length given to GCM")
}
if uint64(len(plaintext)) > ((1<<32)-2)*BlockSize {
panic("cipher: message too large for GCM")
}
ret, out := sliceForAppend(dst, len(plaintext)+g.tagSize)
var counter, tagMask [gcmBlockSize]byte
g.deriveCounter(&counter, nonce)
g.cipher.Encrypt(tagMask[:], counter[:])
gcmInc32(&counter)
g.counterCrypt(out, plaintext, &counter)
g.auth(out[len(plaintext):], out[:len(plaintext)], data, &tagMask)
return ret
}
// Open authenticates and decrypts ciphertext. See the cipher.AEAD interface
// for details.
func (g *gcmAsm) Open(dst, nonce, ciphertext, data []byte) ([]byte, error) {
if len(nonce) != g.nonceSize {
panic("cipher: incorrect nonce length given to GCM")
}
if len(ciphertext) < g.tagSize {
return nil, errOpen
}
if uint64(len(ciphertext)) > ((1<<32)-2)*uint64(BlockSize)+uint64(g.tagSize) {
return nil, errOpen
}
tag := ciphertext[len(ciphertext)-g.tagSize:]
ciphertext = ciphertext[:len(ciphertext)-g.tagSize]
var counter, tagMask [gcmBlockSize]byte
g.deriveCounter(&counter, nonce)
g.cipher.Encrypt(tagMask[:], counter[:])
gcmInc32(&counter)
var expectedTag [gcmTagSize]byte
g.auth(expectedTag[:], ciphertext, data, &tagMask)
ret, out := sliceForAppend(dst, len(ciphertext))
if subtle.ConstantTimeCompare(expectedTag[:g.tagSize], tag) != 1 {
for i := range out {
out[i] = 0
}
return nil, errOpen
}
g.counterCrypt(out, ciphertext, &counter)
return ret, nil
}
func gcmLengths(len0, len1 uint64) [16]byte {
return [16]byte{
byte(len0 >> 56),
byte(len0 >> 48),
byte(len0 >> 40),
byte(len0 >> 32),
byte(len0 >> 24),
byte(len0 >> 16),
byte(len0 >> 8),
byte(len0),
byte(len1 >> 56),
byte(len1 >> 48),
byte(len1 >> 40),
byte(len1 >> 32),
byte(len1 >> 24),
byte(len1 >> 16),
byte(len1 >> 8),
byte(len1),
}
}