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wrap_pad.go
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wrap_pad.go
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package cipher
import (
"bytes"
"crypto/cipher"
)
type wrapPad struct {
b cipher.Block
blockSize int
iv []byte
}
func newWrapPad(b cipher.Block, iv []byte) *wrapPad {
c := &wrapPad{
b: b,
blockSize: b.BlockSize(),
iv: make([]byte, b.BlockSize()),
}
if iv == nil {
iv = defaultAiv
}
if len(iv) < 4 {
panic("cryptobin/wrapPad: IV length must gt or equal 4 bytes")
}
copy(c.iv, iv)
return c
}
type wrapPadEncrypter wrapPad
type wrapPadEncAble interface {
NewWrapPadEncrypter(iv []byte) cipher.BlockMode
}
func NewWrapPadEncrypter(b cipher.Block, iv []byte) cipher.BlockMode {
if wrapPad, ok := b.(wrapPadEncAble); ok {
return wrapPad.NewWrapPadEncrypter(iv)
}
return (*wrapPadEncrypter)(newWrapPad(b, iv))
}
func (x *wrapPadEncrypter) BlockSize() int {
return x.blockSize
}
/** Wrapping according to RFC 5649 section 4.1.
*
* @param[in] icv (Non-standard) IV, 4 bytes. NULL = use default_aiv.
* @param[out] dst Ciphertext. Minimal buffer length = (srclen + 15) bytes.
* Input and output buffers can overlap if block function
* supports that.
* @param[in] src Plaintext as n 64-bit blocks, n >= 2.
*/
func (x *wrapPadEncrypter) CryptBlocks(dst, src []byte) {
if len(src)%8 != 0 {
panic("cryptobin/wrapPad: input not full blocks")
}
if len(dst) < len(src)+8 {
panic("cryptobin/wrapPad: output smaller than input")
}
icv := x.iv
inlen := len(src)
/* n: number of 64-bit blocks in the padded key data
*
* If length of plain text is not a multiple of 8, pad the plain text octet
* string on the right with octets of zeros, where final length is the
* smallest multiple of 8 that is greater than length of plain text.
* If length of plain text is a multiple of 8, then there is no padding. */
var blocks_padded = (inlen + 7) / 8 /* CEILING(m/8) */
var padded_len = blocks_padded * 8
/* RFC 5649 section 3: Alternative Initial Value */
var aiv [8]byte
/* Section 1: use 32-bit fixed field for plaintext octet length */
if inlen == 0 || uint64(inlen) >= WRAP_MAX {
return
}
/* Section 3: Alternative Initial Value */
copy(aiv[:], icv[:4]); /* Standard doesn't mention this. */
aiv[4] = byte((inlen >> 24) & 0xFF)
aiv[5] = byte((inlen >> 16) & 0xFF)
aiv[6] = byte((inlen >> 8) & 0xFF)
aiv[7] = byte(inlen & 0xFF)
if len(dst) < (padded_len + len(aiv)) {
panic("cryptobin/wrapPad: output too small")
}
if padded_len == 8 {
/*
* Section 4.1 - special case in step 2: If the padded plaintext
* contains exactly eight octets, then prepend the AIV and encrypt
* the resulting 128-bit block using AES in ECB mode.
*/
copy(dst[8:], src)
copy(dst, aiv[:8])
x.b.Encrypt(dst, dst)
} else {
NewWrapEncrypter(x.b, aiv[:]).CryptBlocks(dst, src)
}
copy(x.iv, icv)
}
func (x *wrapPadEncrypter) SetIV(iv []byte) {
if len(iv) != len(x.iv) {
panic("cryptobin/wrapPad: incorrect length IV")
}
copy(x.iv, iv)
}
type wrapPadDecrypter wrapPad
type wrapPadDecAble interface {
NewWrapPadDecrypter(iv []byte) cipher.BlockMode
}
func NewWrapPadDecrypter(b cipher.Block, iv []byte) cipher.BlockMode {
if wrapPad, ok := b.(wrapPadDecAble); ok {
return wrapPad.NewWrapPadDecrypter(iv)
}
return (*wrapPadDecrypter)(newWrapPad(b, iv))
}
func (x *wrapPadDecrypter) BlockSize() int {
return x.blockSize
}
/** Unwrapping according to RFC 5649 section 4.2.
*
* @param[in] icv (Non-standard) IV, 4 bytes. NULL = use default_aiv.
* @param[out] dst Plaintext. Minimal buffer length = (srclen - 8) bytes.
* Input and output buffers can overlap if block function
* supports that.
* @param[in] src Ciphertext as n 64-bit blocks.
*/
func (x *wrapPadDecrypter) CryptBlocks(dst, src []byte) {
if len(src)%8 != 0 {
panic("cryptobin/wrapPad: input not full blocks")
}
if len(dst) < len(src)-8 {
panic("cryptobin/wrapPad: output smaller than input")
}
if len(src) == 0 {
return
}
icv := x.iv
inlen := len(src)
empty := make([]byte, inlen-8)
/* n: number of 64-bit blocks in the padded key data */
var n int = inlen / 8 - 1
var padded_len int
var padding_len int
var ptext_len uint32
/* RFC 5649 section 3: Alternative Initial Value */
var aiv [8]byte = [8]byte{}
var zeros [8]byte = [8]byte{}
/* Section 4.2: Ciphertext length has to be (n+1) 64-bit blocks. */
if (((inlen & 0x7) != 0) || (inlen < 16) || (uint64(inlen) > WRAP_MAX)) {
return
}
if inlen == 16 {
/*
* Section 4.2 - special case in step 1: When n=1, the ciphertext
* contains exactly two 64-bit blocks and they are decrypted as a
* single AES block using AES in ECB mode: AIV | P[1] = DEC(K, C[0] |
* C[1])
*/
var buff [16]byte
x.b.Decrypt(buff[:], src)
copy(aiv[:], buff[:8])
/* Remove AIV */
copy(dst, buff[8:16])
} else {
padded_len = inlen - 8
iv := make([]byte, 8)
wd := NewWrapDecrypter(x.b, iv)
retiv, err := wd.(*wrapDecrypter).cryptBlocks(dst, src)
if err != nil {
copy(dst, empty)
return
}
copy(aiv[:], retiv)
}
/*
* Section 3: AIV checks: Check that MSB(32,A) = A65959A6. Optionally a
* user-supplied value can be used (even if standard doesn't mention
* this).
*/
if !bytes.Equal(aiv[:4], icv[:4]) {
copy(dst, empty)
return
}
/*
* Check that 8*(n-1) < LSB(32,AIV) <= 8*n. If so, let ptext_len =
* LSB(32,AIV).
*/
ptext_len = (uint32(aiv[4]) << 24) |
(uint32(aiv[5]) << 16) |
(uint32(aiv[6]) << 8) |
uint32(aiv[7])
if (8 * (uint32(n) - 1) >= ptext_len || ptext_len > 8 * uint32(n)) {
copy(dst, empty)
return
}
/*
* Check that the rightmost padding_len octets of the output data are
* zero.
*/
padding_len = padded_len - int(ptext_len)
if len(dst) > int(ptext_len) && bytes.Equal(dst[ptext_len:], zeros[:padding_len]) {
copy(dst, empty)
return
}
copy(x.iv, icv)
}
func (x *wrapPadDecrypter) SetIV(iv []byte) {
if len(iv) != len(x.iv) {
panic("cryptobin/wrapPad: incorrect length IV")
}
copy(x.iv, iv)
}