128bitのAES暗号化復号化をC言語で実装してみる。ちょっと理解を深めるためにできるだけ自分で、そして、すべて8bit単位で計算するコードにする。とはいえこんなもの自分で実装する必要はない。が、勉強のためです。
参考サイト
FIPS 197, Advanced Encryption Standard (AES)
ピイジェイさん
#include <stdio.h>
#include <stdint.h>
uint8_t S[16][16]={
{0x63,0x7c,0x77,0x7b,0xf2,0x6b,0x6f,0xc5,0x30,0x01,0x67,0x2b,0xfe,0xd7,0xab,0x76},
{0xca,0x82,0xc9,0x7d,0xfa,0x59,0x47,0xf0,0xad,0xd4,0xa2,0xaf,0x9c,0xa4,0x72,0xc0},
{0xb7,0xfd,0x93,0x26,0x36,0x3f,0xf7,0xcc,0x34,0xa5,0xe5,0xf1,0x71,0xd8,0x31,0x15},
{0x04,0xc7,0x23,0xc3,0x18,0x96,0x05,0x9a,0x07,0x12,0x80,0xe2,0xeb,0x27,0xb2,0x75},
{0x09,0x83,0x2c,0x1a,0x1b,0x6e,0x5a,0xa0,0x52,0x3b,0xd6,0xb3,0x29,0xe3,0x2f,0x84},
{0x53,0xd1,0x00,0xed,0x20,0xfc,0xb1,0x5b,0x6a,0xcb,0xbe,0x39,0x4a,0x4c,0x58,0xcf},
{0xd0,0xef,0xaa,0xfb,0x43,0x4d,0x33,0x85,0x45,0xf9,0x02,0x7f,0x50,0x3c,0x9f,0xa8},
{0x51,0xa3,0x40,0x8f,0x92,0x9d,0x38,0xf5,0xbc,0xb6,0xda,0x21,0x10,0xff,0xf3,0xd2},
{0xcd,0x0c,0x13,0xec,0x5f,0x97,0x44,0x17,0xc4,0xa7,0x7e,0x3d,0x64,0x5d,0x19,0x73},
{0x60,0x81,0x4f,0xdc,0x22,0x2a,0x90,0x88,0x46,0xee,0xb8,0x14,0xde,0x5e,0x0b,0xdb},
{0xe0,0x32,0x3a,0x0a,0x49,0x06,0x24,0x5c,0xc2,0xd3,0xac,0x62,0x91,0x95,0xe4,0x79},
{0xe7,0xc8,0x37,0x6d,0x8d,0xd5,0x4e,0xa9,0x6c,0x56,0xf4,0xea,0x65,0x7a,0xae,0x08},
{0xba,0x78,0x25,0x2e,0x1c,0xa6,0xb4,0xc6,0xe8,0xdd,0x74,0x1f,0x4b,0xbd,0x8b,0x8a},
{0x70,0x3e,0xb5,0x66,0x48,0x03,0xf6,0x0e,0x61,0x35,0x57,0xb9,0x86,0xc1,0x1d,0x9e},
{0xe1,0xf8,0x98,0x11,0x69,0xd9,0x8e,0x94,0x9b,0x1e,0x87,0xe9,0xce,0x55,0x28,0xdf},
{0x8c,0xa1,0x89,0x0d,0xbf,0xe6,0x42,0x68,0x41,0x99,0x2d,0x0f,0xb0,0x54,0xbb,0x16}
};
uint8_t invS[16][16]={
{0x52,0x09,0x6a,0xd5,0x30,0x36,0xa5,0x38,0xbf,0x40,0xa3,0x9e,0x81,0xf3,0xd7,0xfb},
{0x7c,0xe3,0x39,0x82,0x9b,0x2f,0xff,0x87,0x34,0x8e,0x43,0x44,0xc4,0xde,0xe9,0xcb},
{0x54,0x7b,0x94,0x32,0xa6,0xc2,0x23,0x3d,0xee,0x4c,0x95,0x0b,0x42,0xfa,0xc3,0x4e},
{0x08,0x2e,0xa1,0x66,0x28,0xd9,0x24,0xb2,0x76,0x5b,0xa2,0x49,0x6d,0x8b,0xd1,0x25},
{0x72,0xf8,0xf6,0x64,0x86,0x68,0x98,0x16,0xd4,0xa4,0x5c,0xcc,0x5d,0x65,0xb6,0x92},
{0x6c,0x70,0x48,0x50,0xfd,0xed,0xb9,0xda,0x5e,0x15,0x46,0x57,0xa7,0x8d,0x9d,0x84},
{0x90,0xd8,0xab,0x00,0x8c,0xbc,0xd3,0x0a,0xf7,0xe4,0x58,0x05,0xb8,0xb3,0x45,0x06},
{0xd0,0x2c,0x1e,0x8f,0xca,0x3f,0x0f,0x02,0xc1,0xaf,0xbd,0x03,0x01,0x13,0x8a,0x6b},
{0x3a,0x91,0x11,0x41,0x4f,0x67,0xdc,0xea,0x97,0xf2,0xcf,0xce,0xf0,0xb4,0xe6,0x73},
{0x96,0xac,0x74,0x22,0xe7,0xad,0x35,0x85,0xe2,0xf9,0x37,0xe8,0x1c,0x75,0xdf,0x6e},
{0x47,0xf1,0x1a,0x71,0x1d,0x29,0xc5,0x89,0x6f,0xb7,0x62,0x0e,0xaa,0x18,0xbe,0x1b},
{0xfc,0x56,0x3e,0x4b,0xc6,0xd2,0x79,0x20,0x9a,0xdb,0xc0,0xfe,0x78,0xcd,0x5a,0xf4},
{0x1f,0xdd,0xa8,0x33,0x88,0x07,0xc7,0x31,0xb1,0x12,0x10,0x59,0x27,0x80,0xec,0x5f},
{0x60,0x51,0x7f,0xa9,0x19,0xb5,0x4a,0x0d,0x2d,0xe5,0x7a,0x9f,0x93,0xc9,0x9c,0xef},
{0xa0,0xe0,0x3b,0x4d,0xae,0x2a,0xf5,0xb0,0xc8,0xeb,0xbb,0x3c,0x83,0x53,0x99,0x61},
{0x17,0x2b,0x04,0x7e,0xba,0x77,0xd6,0x26,0xe1,0x69,0x14,0x63,0x55,0x21,0x0c,0x7d}
};
uint8_t w[11][16];
uint8_t Rcon[10]={0x01,0x02,0x04,0x08,0x10,0x20,0x40,0x80,0x1b,0x36};
void SubWord(uint8_t* in){
int i;
for(i=0;i<4;i++){
in[i]=S[(in[i]>>4)&0x0F][(in[i]>>0)&0x0F];
}
}
void RotWord(uint8_t* in){
uint8_t tmp;
tmp=in[0];
in[0]=in[1];
in[1]=in[2];
in[2]=in[3];
in[3]=tmp;
}
void KeyExpansion_Single(uint8_t num){
uint8_t i,j;
for(i=0;i<4;i++){
w[num][i]=w[num-1][12+i];
}
RotWord(&(w[num][0]));
SubWord(&(w[num][0]));
w[num][0]^=Rcon[num-1];
for(i=0;i<4;i++){
w[num][i]^=w[num-1][i];
w[num][i+4]=w[num][i]^w[num-1][i+4];
w[num][i+8]=w[num][i+4]^w[num-1][i+8];
w[num][i+12]=w[num][i+8]^w[num-1][i+12];
}
}
void KeyExpansion(uint8_t *key){
uint8_t i;
for(i=0;i<16;i++){
w[0][i]=key[i];
}
for(i=1;i<11;i++){
KeyExpansion_Single(i);
}
}
void AddRoundKey(uint8_t* src,uint8_t nRound){
uint8_t i;
for(i=0;i<16;i++){
src[i]^=w[nRound][i];
}
}
void SubBytes(uint8_t* src){
uint8_t i;
for(i=0;i<16;i++){
src[i]=S[(src[i]>>4)&0x0F][(src[i]>>0)&0x0F];
}
}
void invSubBytes(uint8_t* src){
uint8_t i;
for(i=0;i<16;i++){
src[i]=invS[(src[i]>>4)&0x0F][(src[i]>>0)&0x0F];
}
}
void ShiftRows(uint8_t* src){
uint8_t temp[8];
uint8_t i,j;
for(i=0;i<4;i++){
for(j=0;j<4;j++){
temp[j]=src[j*4+i];
temp[j+4]=src[j*4+i];
}
for(j=0;j<4;j++){
src[j*4+i]=temp[j+i];
}
}
}
void invShiftRows(uint8_t* src){
uint8_t temp[8];
uint8_t i,j;
for(i=0;i<4;i++){
for(j=0;j<4;j++){
temp[j]=src[j*4+i];
temp[j+4]=src[j*4+i];
}
for(j=0;j<4;j++){
src[j*4+i]=temp[j+4-i];
}
}
}
uint8_t mul(uint8_t a,uint8_t b){
uint8_t x=0;
uint8_t i;
for(i=0x08;i>0;i>>=1){
if(x&0x80){
x<<=1;
x^=0x1b;
}else{
x<<=1;
}
if(b&i){
x^=a;
}
}
return x;
}
void MixColumn_single(uint8_t *r) {
uint8_t t[4];
uint8_t i;
for(i=0;i<4;i++){
t[i]=r[i];
}
r[0]=mul(t[0],2)^mul(t[1],3)^mul(t[2],1)^mul(t[3],1);
r[1]=mul(t[1],2)^mul(t[2],3)^mul(t[3],1)^mul(t[0],1);
r[2]=mul(t[2],2)^mul(t[3],3)^mul(t[0],1)^mul(t[1],1);
r[3]=mul(t[3],2)^mul(t[0],3)^mul(t[1],1)^mul(t[2],1);
}
void MixColumns(uint8_t* src){
uint8_t i;
for(i=0;i<4;i++){
MixColumn_single(&(src[i*4]));
}
}
void invMixColumn_single(uint8_t *r) {
uint8_t t[4];
uint8_t i;
for(i=0;i<4;i++){
t[i]=r[i];
}
r[0]=mul(t[0],14)^mul(t[1],11)^mul(t[2],13)^mul(t[3],9);
r[1]=mul(t[1],14)^mul(t[2],11)^mul(t[3],13)^mul(t[0],9);
r[2]=mul(t[2],14)^mul(t[3],11)^mul(t[0],13)^mul(t[1],9);
r[3]=mul(t[3],14)^mul(t[0],11)^mul(t[1],13)^mul(t[2],9);
}
void invMixColumns(uint8_t* src){
uint8_t i;
for(i=0;i<4;i++){
invMixColumn_single(&(src[i*4]));
}
}
void Cipher(uint8_t* data,uint8_t* key){
int i;
AddRoundKey(data,0);
for(i=1;i<10;i++){
SubBytes(data);
ShiftRows(data);
MixColumns(data);
AddRoundKey(data,i);
}
SubBytes(data);
ShiftRows(data);
AddRoundKey(data,i);
}
void invCipher(uint8_t* data,uint8_t* key){
int i;
AddRoundKey(data,10);
for(i=9;i>0;i--){
invShiftRows(data);
invSubBytes(data);
AddRoundKey(data,i);
invMixColumns(data);
}
invShiftRows(data);
invSubBytes(data);
AddRoundKey(data,0);
}
int main(int argc,char** argv){
uint8_t key[]={0x00,0x01,0x02,0x03,0x04,0x05,0x06,0x07,0x08,0x09,0x0a,0x0b,0x0c,0x0d,0x0e,0x0f};
uint8_t data[]={0x00,0x11,0x22,0x33,0x44,0x55,0x66,0x77,0x88,0x99,0xaa,0xbb,0xcc,0xdd,0xee,0xff};
int i,j;
KeyExpansion(key);
Cipher(data,key);
for(i=0;i<16;i++){
printf("%02X",data[i]);
}
printf("\n");
invCipher(data,key);
for(i=0;i<16;i++){
printf("%02X",data[i]);
}
printf("\n");
}
できた(๑•̀д•́๑)
相変わらずコメントなし。そして、MixColumnはまぁまぁピイジェイさんのパクリです。説明が異常に難しいんよ。どうするのか見当がつかなかったので。（検算のためテストベクタもピイジェイさんのコード内の値をパクッてます。）
全部8bit(1byte)単位での計算にしたので、まどろっこしいところもあるけど、とりあえずどういう仕組みなのかは見やすくできたと思う。
コメントをお書きください