Skip to content

Instantly share code, notes, and snippets.

@odzhan

odzhan/aes128_cbc.c

Last active October 29, 2023 23:04
Show Gist options
  • Save odzhan/b34491251d28ab743e725c62f3d49858 to your computer and use it in GitHub Desktop.
Save odzhan/b34491251d28ab743e725c62f3d49858 to your computer and use it in GitHub Desktop.
Download ZIP
Simple Implementation of AES-128
Raw
aes128_cbc.c
/**
This is free and unencumbered software released into the public domain.
Anyone is free to copy, modify, publish, use, compile, sell, or
distribute this software, either in source code form or as a compiled
binary, for any purpose, commercial or non-commercial, and by any
means.
In jurisdictions that recognize copyright laws, the author or authors
of this software dedicate any and all copyright interest in the
software to the public domain. We make this dedication for the benefit
of the public at large and to the detriment of our heirs and
successors. We intend this dedication to be an overt act of
relinquishment in perpetuity of all present and future rights to this
software under copyright law.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR
OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
OTHER DEALINGS IN THE SOFTWARE.
For more information, please refer to <http://unlicense.org/> */
#include "aes128_cbc.h"
/**
Encrypt data inplace using AES-128 in CBC mode.
*/
void
aes128_cbc_encrypt(aes128_ctx* c, void* data, u32 len) {
u8 i, *buf = (u8*)data, *iv = c->iv;
while (len) {
// XOR the plaintext with IV or last ciphertext.
for (i = 0; i < AES_BLK_LEN; i++) buf[i] ^= iv[i];
// Encrypt the result.
aes128_ecb_encrypt(c, buf);
// Update length, IV and position.
iv = buf;
len -= AES_BLK_LEN;
buf += AES_BLK_LEN;
}
}
/**
Decrypt data inplace using AES-128 in CBC mode.
*/
void
aes128_cbc_decrypt(aes128_ctx* c, void* data, u32 len) {
u8 i, tmp[AES_BLK_LEN], *buf = (u8*)data, *iv = c->iv;
while (len) {
// Copy ciphertext to local buffer.
for (i = 0; i< AES_BLK_LEN; i++) tmp[i] = buf[i];
// Decrypt ciphertext.
aes128_ecb_decrypt(c, buf);
// XOR the result with IV or last ciphertext.
for (i = 0; i < AES_BLK_LEN; i++) buf[i] ^= iv[i];
// Update length, IV and position.
len -= AES_BLK_LEN;
iv = tmp;
buf += AES_BLK_LEN;
}
}
Raw
aes128_cbc.h
/**
This is free and unencumbered software released into the public domain.
Anyone is free to copy, modify, publish, use, compile, sell, or
distribute this software, either in source code form or as a compiled
binary, for any purpose, commercial or non-commercial, and by any
means.
In jurisdictions that recognize copyright laws, the author or authors
of this software dedicate any and all copyright interest in the
software to the public domain. We make this dedication for the benefit
of the public at large and to the detriment of our heirs and
successors. We intend this dedication to be an overt act of
relinquishment in perpetuity of all present and future rights to this
software under copyright law.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR
OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
OTHER DEALINGS IN THE SOFTWARE.
For more information, please refer to <http://unlicense.org/> */
#ifndef AES128_CBC_H
#define AES128_CBC_H
#include "aes128_ecb.h"
#ifdef __cplusplus
extern "C" {
#endif
void
aes128_cbc_encrypt(aes128_ctx* c, void* data, u32 len);
void
aes128_cbc_decrypt(aes128_ctx* c, void* data, u32 len);
#ifdef __cplusplus
}
#endif
#endif
Raw
aes128_ecb.c
/**
This is free and unencumbered software released into the public domain.
Anyone is free to copy, modify, publish, use, compile, sell, or
distribute this software, either in source code form or as a compiled
binary, for any purpose, commercial or non-commercial, and by any
means.
In jurisdictions that recognize copyright laws, the author or authors
of this software dedicate any and all copyright interest in the
software to the public domain. We make this dedication for the benefit
of the public at large and to the detriment of our heirs and
successors. We intend this dedication to be an overt act of
relinquishment in perpetuity of all present and future rights to this
software under copyright law.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR
OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
OTHER DEALINGS IN THE SOFTWARE.
For more information, please refer to <http://unlicense.org/> */
#include "aes128_ecb.h"
u32
M(u32 x) {
u32 t = x & 0x80808080;
return((x ^ t) << 1) ^ ((t >> 7) * 0x1b);
}
/**
Initialises AES context.
This creates the sbox for encryption and inverse for decryption.
It only needs to be called once.
*/
void
aes128_init_ctx(aes128_ctx* c) {
u32 x=1, i;
u8 gf_exp[256];
// Create lookup table for the exponentiation of the Galois Field (GF)
for (i = 0; i < 256; i++) {
gf_exp[i] = x;
x ^= M(x);
}
// Generate S-box values for each byte (0-255)
c->sbox[0] = 99;
for (i = 0; i < 255; i++) {
x = gf_exp[255 - i];
x |= x << 8;
x ^= (x >> 4) ^ (x >> 5) ^ (x >> 6) ^ (x >> 7);
c->sbox[gf_exp[i]] = (x ^ 99) & 0xFF;
}
// Compute the inverse S-box.
for (i=0; i<256; i++) {
c->sbox_inv[c->sbox[i]] = i;
}
}
/**
Creates round keys for AES-128 encryption.
This should be called after aes128_init_ctx()
*/
void
aes128_set_key(aes128_ctx* c, void* mk) {
u32 i, w, k[4], *rk=(u32*)c->rkeys;
// Copy master key to local buffer
for (i = 0; i < 4; i++) {
k[i] = ((u32*)mk)[i];
}
// Create 10 round keys
for (u32 rc = 1; rc != 216; rc = M(rc)) {
// Copy round key to context
for (i = 0; i < 4; i++) *rk = k[i], rk++;
// First part of ExpandKey
w = k[3];
for (i = 0; i < 4; i++) {
w = (w & -256) | c->sbox[w & 255], w = R(w, 8);
}
// AddConstant
w = R(w, 8) ^ rc;
// Second part of ExpandKey
for (i = 0; i < 4; i++) {
w = k[i] ^= w;
}
}
}
/**
Encrypt data inplace using AES-128 in ECB mode.
*/
void
aes128_ecb_encrypt(aes128_ctx* c, void* data) {
u32 nr=0, i, w, x[4], *s = (u32*)data, *rk=(u32*)c->rkeys;
for (i = 0; i < 4; i++) {
x[i] = s[i];
}
for (;;) {
for (i = 0; i < 4; i++) {
s[i] = x[i] ^ rk[i];
}
if (nr++ == 10) break;
for (w = i = 0; i < 16; i++) {
((u8*)x)[w] = c->sbox[((u8*)s)[i]], w = (w - 3) & 15;
}
if (nr != 10) {
for (i = 0; i < 4; i++) {
w = x[i], x[i] = R(w, 8) ^ R(w, 16) ^ R(w, 24) ^ M(R(w, 8) ^ w);
}
}
}
}
/**
Decrypt data inplace using AES-128 in ECB mode.
*/
void
aes128_ecb_decrypt(aes128_ctx* c, void* data) {
u32 nr=10, i, w, x[4], *s = (u32*)data, *rk=(u32*)c->rkeys[10];
// AddRoundKey
for (i = 0; i < 4; i++) {
s[i] ^= rk[i];
}
// Loop ten times
for (;;) {
// Subtract 16-bytes from round keys buffer.
rk -= 4;
// InvShiftRows
for (w = 0, i = 15; (int)i>=0; i--) {
w = (w + 3) & 15, ((u8*)x)[i] = ((u8*)s)[w];
}
// InvSubBytes
for (w = i = 0; i < 16; i++) {
((u8*)s)[i] = c->sbox_inv[((u8*)x)[i]];
}
// AddRoundKey
for (i = 0; i < 4; i++) {
s[i] ^= rk[i];
}
if (--nr == 0) break;
// InvMixColumns
for (i = 0; i < 4; i++) {
w = s[i], w ^= M(M(R(w, 16) ^ w));
s[i] = R(w, 8) ^ R(w, 16) ^ R(w, 24) ^ M(R(w, 8) ^ w);
}
}
}
Raw
aes128_ecb.h
/**
This is free and unencumbered software released into the public domain.
Anyone is free to copy, modify, publish, use, compile, sell, or
distribute this software, either in source code form or as a compiled
binary, for any purpose, commercial or non-commercial, and by any
means.
In jurisdictions that recognize copyright laws, the author or authors
of this software dedicate any and all copyright interest in the
software to the public domain. We make this dedication for the benefit
of the public at large and to the detriment of our heirs and
successors. We intend this dedication to be an overt act of
relinquishment in perpetuity of all present and future rights to this
software under copyright law.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR
OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
OTHER DEALINGS IN THE SOFTWARE.
For more information, please refer to <http://unlicense.org/> */
#ifndef AES128_ECB_H
#define AES128_ECB_H
#define AES_KEY_LEN 16 // 128-bit
#define AES_BLK_LEN 16 // Always 16 for 128-bit blocks
#define AES_IV_LEN 16 // Always 16 for 128-bit blocks
#define R(v,n)(((v)>>(n))|((v)<<(32-(n))))
typedef unsigned char u8;
typedef unsigned int u32;
typedef struct _aes128_ctx {
u8 sbox[256];
u8 sbox_inv[256];
u8 iv[AES_IV_LEN];
u8 rkeys[11][AES_KEY_LEN];
} aes128_ctx;
#ifdef __cplusplus
extern "C" {
#endif
void
aes128_init_ctx(aes128_ctx* c);
void
aes128_set_key(aes128_ctx* c, void* mk);
void
aes128_ecb_encrypt(aes128_ctx* c, void* data);
void
aes128_ecb_decrypt(aes128_ctx* c, void* data);
#ifdef __cplusplus
}
#endif
#endif
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment