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312
MITM/aes-gcm.c
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312
MITM/aes-gcm.c
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#include "aes.h"
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static void inc32(aes_uchar *block)
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{
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aes_uint val;
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val = AES_GET_BE32(block + AES_BLOCK_SIZE - 4);
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val++;
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AES_PUT_BE32(block + AES_BLOCK_SIZE - 4, val);
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}
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static void xor_block(aes_uchar *dst, const aes_uchar *src)
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{
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aes_uint *d = (aes_uint *) dst;
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aes_uint *s = (aes_uint *) src;
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*d++ ^= *s++;
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*d++ ^= *s++;
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*d++ ^= *s++;
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*d++ ^= *s++;
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}
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static void shift_right_block(aes_uchar *v)
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{
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aes_uint val;
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val = AES_GET_BE32(v + 12);
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val >>= 1;
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if (v[11] & 0x01)
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val |= 0x80000000;
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AES_PUT_BE32(v + 12, val);
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val = AES_GET_BE32(v + 8);
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val >>= 1;
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if (v[7] & 0x01)
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val |= 0x80000000;
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AES_PUT_BE32(v + 8, val);
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val = AES_GET_BE32(v + 4);
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val >>= 1;
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if (v[3] & 0x01)
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val |= 0x80000000;
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AES_PUT_BE32(v + 4, val);
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val = AES_GET_BE32(v);
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val >>= 1;
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AES_PUT_BE32(v, val);
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}
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/* Multiplication in GF(2^128) */
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static void gf_mult(const aes_uchar *x, const aes_uchar *y, aes_uchar *z)
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{
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aes_uchar v[16];
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int i, j;
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memset(z, 0, 16); /* Z_0 = 0^128 */
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memcpy(v, y, 16); /* V_0 = Y */
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for (i = 0; i < 16; i++) {
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for (j = 0; j < 8; j++) {
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if (x[i] & 1 << (7 - j)) {
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/* Z_(i + 1) = Z_i XOR V_i */
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xor_block(z, v);
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} else {
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/* Z_(i + 1) = Z_i */
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}
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if (v[15] & 0x01) {
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/* V_(i + 1) = (V_i >> 1) XOR R */
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shift_right_block(v);
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/* R = 11100001 || 0^120 */
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v[0] ^= 0xe1;
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} else {
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/* V_(i + 1) = V_i >> 1 */
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shift_right_block(v);
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}
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}
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}
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}
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static void ghash_start(aes_uchar *y)
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{
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/* Y_0 = 0^128 */
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memset(y, 0, 16);
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}
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static void ghash(const aes_uchar *h, const aes_uchar *x, size_t xlen, aes_uchar *y)
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{
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size_t m, i;
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const aes_uchar *xpos = x;
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aes_uchar tmp[16];
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m = xlen / 16;
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for (i = 0; i < m; i++) {
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/* Y_i = (Y^(i-1) XOR X_i) dot H */
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xor_block(y, xpos);
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xpos += 16;
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/* dot operation:
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* multiplication operation for binary Galois (finite) field of
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* 2^128 elements */
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gf_mult(y, h, tmp);
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memcpy(y, tmp, 16);
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}
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if (x + xlen > xpos) {
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/* Add zero padded last block */
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size_t last = x + xlen - xpos;
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memcpy(tmp, xpos, last);
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memset(tmp + last, 0, sizeof(tmp) - last);
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/* Y_i = (Y^(i-1) XOR X_i) dot H */
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xor_block(y, tmp);
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/* dot operation:
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* multiplication operation for binary Galois (finite) field of
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* 2^128 elements */
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gf_mult(y, h, tmp);
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memcpy(y, tmp, 16);
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}
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/* Return Y_m */
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}
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static void aes_gctr(void *aes, const aes_uchar *icb, const aes_uchar *x, size_t xlen, aes_uchar *y)
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{
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size_t i, n, last;
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aes_uchar cb[AES_BLOCK_SIZE], tmp[AES_BLOCK_SIZE];
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const aes_uchar *xpos = x;
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aes_uchar *ypos = y;
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if (xlen == 0)
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return;
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n = xlen / 16;
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memcpy(cb, icb, AES_BLOCK_SIZE);
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/* Full blocks */
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for (i = 0; i < n; i++) {
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aes_encrypt(aes, cb, ypos);
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xor_block(ypos, xpos);
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xpos += AES_BLOCK_SIZE;
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ypos += AES_BLOCK_SIZE;
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inc32(cb);
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}
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last = x + xlen - xpos;
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if (last) {
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/* Last, partial block */
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aes_encrypt(aes, cb, tmp);
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for (i = 0; i < last; i++)
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*ypos++ = *xpos++ ^ tmp[i];
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}
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}
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static void * aes_gcm_init_hash_subkey(const aes_uchar *key, size_t key_len, aes_uchar *H)
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{
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void *aes;
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aes = aes_encrypt_init(key, key_len);
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if (aes == NULL)
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return NULL;
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/* Generate hash subkey H = AES_K(0^128) */
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memset(H, 0, AES_BLOCK_SIZE);
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aes_encrypt(aes, H, H);
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aes_hexdump_key(MSG_EXCESSIVE, "Hash subkey H for GHASH", H, AES_BLOCK_SIZE);
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return aes;
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}
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static void aes_gcm_prepare_j0(const aes_uchar *iv, size_t iv_len, const aes_uchar *H, aes_uchar *J0)
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{
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aes_uchar len_buf[16];
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if (iv_len == 12) {
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/* Prepare block J_0 = IV || 0^31 || 1 [len(IV) = 96] */
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memcpy(J0, iv, iv_len);
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memset(J0 + iv_len, 0, AES_BLOCK_SIZE - iv_len);
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J0[AES_BLOCK_SIZE - 1] = 0x01;
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} else {
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/*
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* s = 128 * ceil(len(IV)/128) - len(IV)
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* J_0 = GHASH_H(IV || 0^(s+64) || [len(IV)]_64)
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*/
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ghash_start(J0);
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ghash(H, iv, iv_len, J0);
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AES_PUT_BE64(len_buf, 0);
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AES_PUT_BE64(len_buf + 8, iv_len * 8);
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ghash(H, len_buf, sizeof(len_buf), J0);
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}
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}
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static void aes_gcm_gctr(void *aes, const aes_uchar *J0, const aes_uchar *in, size_t len,
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aes_uchar *out)
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{
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aes_uchar J0inc[AES_BLOCK_SIZE];
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if (len == 0)
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return;
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memcpy(J0inc, J0, AES_BLOCK_SIZE);
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inc32(J0inc);
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aes_gctr(aes, J0inc, in, len, out);
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}
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static void aes_gcm_ghash(const aes_uchar *H, const aes_uchar *aad, size_t aad_len,
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const aes_uchar *crypt, size_t crypt_len, aes_uchar *S)
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{
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aes_uchar len_buf[16];
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/*
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* u = 128 * ceil[len(C)/128] - len(C)
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* v = 128 * ceil[len(A)/128] - len(A)
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* S = GHASH_H(A || 0^v || C || 0^u || [len(A)]64 || [len(C)]64)
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* (i.e., zero padded to block size A || C and lengths of each in bits)
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*/
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ghash_start(S);
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ghash(H, aad, aad_len, S);
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ghash(H, crypt, crypt_len, S);
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AES_PUT_BE64(len_buf, aad_len * 8);
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AES_PUT_BE64(len_buf + 8, crypt_len * 8);
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ghash(H, len_buf, sizeof(len_buf), S);
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aes_hexdump_key(MSG_EXCESSIVE, "S = GHASH_H(...)", S, 16);
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}
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/**
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* aes_gcm_ae - GCM-AE_K(IV, P, A)
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*/
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int aes_gcm_ae(const aes_uchar *key, size_t key_len, const aes_uchar *iv, size_t iv_len,
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const aes_uchar *plain, size_t plain_len,
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const aes_uchar *aad, size_t aad_len, aes_uchar *crypt, aes_uchar *tag)
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{
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aes_uchar H[AES_BLOCK_SIZE];
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aes_uchar J0[AES_BLOCK_SIZE];
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aes_uchar S[16];
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void *aes;
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aes = aes_gcm_init_hash_subkey(key, key_len, H);
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if (aes == NULL)
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return -1;
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aes_gcm_prepare_j0(iv, iv_len, H, J0);
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/* C = GCTR_K(inc_32(J_0), P) */
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aes_gcm_gctr(aes, J0, plain, plain_len, crypt);
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aes_gcm_ghash(H, aad, aad_len, crypt, plain_len, S);
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/* T = MSB_t(GCTR_K(J_0, S)) */
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aes_gctr(aes, J0, S, sizeof(S), tag);
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/* Return (C, T) */
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aes_encrypt_deinit(aes);
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return 0;
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}
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/**
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* aes_gcm_ad - GCM-AD_K(IV, C, A, T)
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*/
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int aes_gcm_ad(const aes_uchar *key, size_t key_len, const aes_uchar *iv, size_t iv_len,
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const aes_uchar *crypt, size_t crypt_len,
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const aes_uchar *aad, size_t aad_len, const aes_uchar *tag, aes_uchar *plain)
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{
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aes_uchar H[AES_BLOCK_SIZE];
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aes_uchar J0[AES_BLOCK_SIZE];
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aes_uchar S[16], T[16];
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void *aes;
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aes = aes_gcm_init_hash_subkey(key, key_len, H);
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if (aes == NULL)
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return -1;
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aes_gcm_prepare_j0(iv, iv_len, H, J0);
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/* P = GCTR_K(inc_32(J_0), C) */
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aes_gcm_gctr(aes, J0, crypt, crypt_len, plain);
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aes_gcm_ghash(H, aad, aad_len, crypt, crypt_len, S);
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/* T' = MSB_t(GCTR_K(J_0, S)) */
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aes_gctr(aes, J0, S, sizeof(S), T);
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aes_encrypt_deinit(aes);
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if (memcmp(tag, T, 16) != 0) {
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aes_printf(MSG_EXCESSIVE, "GCM: Tag mismatch");
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return -1;
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}
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return 0;
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}
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int aes_gmac(const aes_uchar *key, size_t key_len, const aes_uchar *iv, size_t iv_len,
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const aes_uchar *aad, size_t aad_len, aes_uchar *tag)
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{
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return aes_gcm_ae(key, key_len, iv, iv_len, NULL, 0, aad, aad_len, NULL, tag);
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}
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