yaole
150 lines
3.7 KiB
Go
150 lines
3.7 KiB
Go
package blockmode
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import (
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"fmt"
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"xdx.jelly/xgcl/gerrors"
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"xdx.jelly/xgcl/internal/subtle"
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"xdx.jelly/xgcl/internal/xor"
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)
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// Counter (CTR) mode.
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// CTR converts a block cipher into a stream cipher by
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// repeatedly encrypting an incrementing counter and
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// xoring the resulting stream of data with the input.
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// See NIST SP 800-38A, pp 13-15
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type ctr struct {
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b EcbBlockMode
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ctr []byte //counter
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out []byte // out[outUsed:] is the unused encrypted counters.
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outUsed int
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}
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const streamBufferSize = 4096
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// ctrAble is an interface implemented by ciphers that have a specific optimized
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// implementation of CTR, like crypto/aes. NewCTR will check for this interface
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// and return the specific Stream if found.
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type ctrAble interface {
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NewCTR(iv []byte) (TernaryStream, error)
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}
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// NewCTR returns a Stream which encrypts/decrypts using the given Block in
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// counter mode. The length of iv must be the same as the Block's block size.
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func NewCTR(block EcbBlockMode, iv []byte) (TernaryStream, error) {
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if ctr, ok := block.(ctrAble); ok {
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return ctr.NewCTR(iv)
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}
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if len(iv) != block.BlockSize() {
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return nil, gerrors.WithAnnotatingf(ErrInvalidIV, "input IV length(%d) must be %d bytes", len(iv), block.BlockSize())
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}
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bufSize := streamBufferSize
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if bufSize < block.BlockSize() {
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bufSize = block.BlockSize()
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}
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return &ctr{
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b: block,
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ctr: dup(iv),
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out: make([]byte, 0, bufSize),
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outUsed: 0,
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}, nil
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}
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func (x *ctr) reset(iv []byte) error {
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if len(iv) != x.b.BlockSize() {
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return gerrors.WithAnnotatingf(ErrInvalidIV, "input IV length(%d) must be %d bytes", len(iv), x.b.BlockSize())
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}
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copy(x.ctr, iv)
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x.out = x.out[:0]
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x.outUsed = 0
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return nil
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}
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// refill 填充x.out.
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func (x *ctr) refill() {
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begin := len(x.out) - x.outUsed
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copy(x.out, x.out[x.outUsed:])
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x.out = x.out[:cap(x.out)]
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bs := x.b.BlockSize()
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end := begin
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for end <= len(x.out)-bs {
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copy(x.out[end:], x.ctr)
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end += bs
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for i := len(x.ctr) - 1; i >= 0; i-- {
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x.ctr[i]++
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if x.ctr[i] != 0 {
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break
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}
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}
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}
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_ = x.b.EcbEncCryptBlocks(x.out[begin:end], x.out[begin:end])
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x.out = x.out[:end]
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x.outUsed = 0
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}
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func (x *ctr) XORKeyStream(dst, src []byte) {
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if len(dst) < len(src) {
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// By definition of cipher.Stream, if len(dst) < len(src), XORKeyStream should panic.
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panic(fmt.Sprintf("length of output buf(%d) less than the input(%d)", len(dst), len(src)))
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}
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if subtle.InexactOverlap(dst[:len(src)], src) {
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panic("ctr.XORKeyStream: dst must be exact overlap with src or non-overlap with src")
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}
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for len(src) > 0 {
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if x.outUsed >= len(x.out)-x.b.BlockSize() {
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x.refill()
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}
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n := xor.XorBytes(dst, src, x.out[x.outUsed:])
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dst = dst[n:]
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src = src[n:]
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x.outUsed += n
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}
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}
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var _ TernaryStream = &ctr{}
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// EncryptInit implements TernaryStream
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func (x *ctr) EncryptInit(iv []byte) error {
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return x.reset(iv)
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}
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// Encrypt implements TernaryStream
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func (x *ctr) Encrypt(dst []byte, in []byte) ([]byte, error) {
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ret, out := sliceForAppend(dst, len(in))
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x.XORKeyStream(out, in)
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return ret, nil
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}
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// EncryptFinal implements TernaryStream
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func (x *ctr) EncryptFinal(dst []byte) ([]byte, error) {
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return dst, nil
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}
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// EncryptUpdate implements TernaryStream
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func (x *ctr) EncryptUpdate(dst []byte, in []byte) ([]byte, error) {
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return x.Encrypt(dst, in)
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}
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// Decrypt implements TernaryStream
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func (x *ctr) Decrypt(dst []byte, in []byte) ([]byte, error) {
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return x.Encrypt(dst, in)
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}
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// DecryptFinal implements TernaryStream
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func (x *ctr) DecryptFinal(dst []byte) ([]byte, error) {
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return dst, nil
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}
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// DecryptInit implements TernaryStream
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func (x *ctr) DecryptInit(iv []byte) error {
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return x.reset(iv)
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}
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// DecryptUpdate implements TernaryStream
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func (x *ctr) DecryptUpdate(dst []byte, in []byte) ([]byte, error) {
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return x.Encrypt(dst, in)
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}
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