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authorIndrajith K L2022-12-03 17:00:20 +0530
committerIndrajith K L2022-12-03 17:00:20 +0530
commitf5c4671bfbad96bf346bd7e9a21fc4317b4959df (patch)
tree2764fc62da58f2ba8da7ed341643fc359873142f /v_windows/v/vlib/crypto/aes/aes_cbc.v
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Diffstat (limited to 'v_windows/v/vlib/crypto/aes/aes_cbc.v')
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1 files changed, 126 insertions, 0 deletions
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+// Copyright (c) 2019-2021 Alexander Medvednikov. All rights reserved.
+// Use of this source code is governed by an MIT license
+// that can be found in the LICENSE file.
+// Cipher block chaining (CBC) mode.
+// CBC provides confidentiality by xoring (chaining) each plaintext block
+// with the previous ciphertext block before applying the block cipher.
+// See NIST SP 800-38A, pp 10-11
+// NOTE this will be moved to crypto.cipher interface (joe-c)
+module aes
+
+import crypto.cipher
+import crypto.internal.subtle
+
+struct AesCbc {
+mut:
+ b AesCipher
+ block_size int
+ iv []byte
+ tmp []byte
+}
+
+// internal
+fn new_aes_cbc(b AesCipher, iv []byte) AesCbc {
+ return AesCbc{
+ b: b
+ block_size: b.block_size()
+ iv: iv.clone()
+ tmp: []byte{len: (b.block_size())}
+ }
+}
+
+// new_cbc returns a `AesCbc` which encrypts in cipher block chaining
+// mode, using the given Block. The length of iv must be the same as the
+// Block's block size.
+pub fn new_cbc(b AesCipher, iv []byte) AesCbc {
+ if iv.len != b.block_size() {
+ panic('crypto.cipher.new_cbc_encrypter: IV length must equal block size')
+ }
+ return new_aes_cbc(b, iv)
+}
+
+// block_size returns the block size of the checksum in bytes.
+pub fn (x &AesCbc) block_size() int {
+ return x.block_size
+}
+
+// encrypt_blocks encrypts the blocks in `src_` to `dst_`.
+// Please note: `dst_` is mutable for performance reasons.
+pub fn (x &AesCbc) encrypt_blocks(mut dst_ []byte, src_ []byte) {
+ unsafe {
+ mut dst := *dst_
+ mut src := src_
+ if src.len % x.block_size != 0 {
+ panic('crypto.cipher: input not full blocks')
+ }
+ if dst.len < src.len {
+ panic('crypto.cipher: output smaller than input')
+ }
+ if subtle.inexact_overlap(dst[..src.len], src_) {
+ panic('crypto.cipher: invalid buffer overlap')
+ }
+ mut iv := x.iv
+ for src.len > 0 {
+ // Write the xor to dst, then encrypt in place.
+ cipher.xor_bytes(mut dst[..x.block_size], src[..x.block_size], iv)
+ x.b.encrypt(mut dst[..x.block_size], mut dst[..x.block_size])
+ // Move to the next block with this block as the next iv.
+ iv = dst[..x.block_size]
+ if x.block_size >= src.len {
+ src = []
+ } else {
+ src = src[x.block_size..]
+ }
+ dst = dst[x.block_size..]
+ }
+ // Save the iv for the next crypt_blocks call.
+ copy(x.iv, iv)
+ }
+}
+
+// decrypt_blocks decrypts the blocks in `src` to `dst`.
+// Please note: `dst` is mutable for performance reasons.
+pub fn (mut x AesCbc) decrypt_blocks(mut dst []byte, src []byte) {
+ if src.len % x.block_size != 0 {
+ panic('crypto.cipher: input not full blocks')
+ }
+ if dst.len < src.len {
+ panic('crypto.cipher: output smaller than input')
+ }
+ if subtle.inexact_overlap((*dst)[..src.len], src) {
+ panic('crypto.cipher: invalid buffer overlap')
+ }
+ if src.len == 0 {
+ return
+ }
+ // For each block, we need to xor the decrypted data with the previous block's ciphertext (the iv).
+ // To avoid making a copy each time, we loop over the blocks BACKWARDS.
+ mut end := src.len
+ mut start := end - x.block_size
+ mut prev := start - x.block_size
+ // Copy the last block of ciphertext in preparation as the new iv.
+ copy(x.tmp, src[start..end])
+ // Loop over all but the first block.
+ for start > 0 {
+ mut src_chunk := src[start..end]
+ x.b.decrypt(mut (*dst)[start..end], mut src_chunk)
+ cipher.xor_bytes(mut (*dst)[start..end], (*dst)[start..end], src[prev..start])
+ end = start
+ start = prev
+ prev -= x.block_size
+ }
+ // The first block is special because it uses the saved iv.
+ mut src_chunk := src[start..end]
+ x.b.decrypt(mut (*dst)[start..end], mut src_chunk)
+ cipher.xor_bytes(mut (*dst)[start..end], (*dst)[start..end], x.iv)
+ // Set the new iv to the first block we copied earlier.
+ x.iv = x.tmp
+ x.tmp = x.iv
+}
+
+fn (x &AesCbc) set_iv(iv []byte) {
+ if iv.len != x.iv.len {
+ panic('cipher: incorrect length IV')
+ }
+ copy(x.iv, iv)
+}