Problem - Kevin Tafuro

void spc_pctr_do_odd(SPC_CTR2_CTX *ctx) {
size_t i, j;
unsigned char final[SPC_BLOCK_SZ];
for (i = 0; i + SPC_BLOCK_SZ < ctx->len; i += 2 * SPC_BLOCK_SZ) {
SPC_DO_ENCRYPT(&(ctx->ks), ctx->ctr_odd, ctx->outptr_odd);
pctr_increment(ctx->ctr_odd);
pctr_increment(ctx->ctr_odd);
for (j = 0; j < SPC_BLOCK_SZ / sizeof(int); j++)
((int *)ctx->outptr_odd)[j] ^= ((int *)ctx->inptr_odd)[j];
ctx->outptr_odd += SPC_BLOCK_SZ * 2;
ctx->inptr_odd += SPC_BLOCK_SZ * 2;
}
if (i < ctx->len) {
SPC_DO_ENCRYPT(&(ctx->ks), ctx->ctr_odd, final);
for (j = 0; j < ctx->len - i; j++)
ctx->outptr_odd[j] = final[j] ^ ctx->inptr_odd[j];
}
}
void spc_pctr_do_even(SPC_CTR2_CTX *ctx) {
size_t i, j;
unsigned char final[SPC_BLOCK_SZ];
for (i = SPC_BLOCK_SZ; i + SPC_BLOCK_SZ < ctx->len; i += 2 * SPC_BLOCK_SZ) {
SPC_DO_ENCRYPT(&(ctx->ks), ctx->ctr_even, ctx->outptr_even);
pctr_increment(ctx->ctr_even);
pctr_increment(ctx->ctr_even);
for (j = 0; j < SPC_BLOCK_SZ / sizeof(int); j++)
((int *)ctx->outptr_even)[j] ^= ((int *)ctx->inptr_even)[j];
ctx->outptr_even += SPC_BLOCK_SZ * 2;
ctx->inptr_even += SPC_BLOCK_SZ * 2;
}
if (i < ctx->len) {
SPC_DO_ENCRYPT(&(ctx->ks), ctx->ctr_even, final);
for (j = 0; j < ctx->len - i; j++)
ctx->outptr_even[j] = final[j] ^ ctx->inptr_even[j];
}
}
int spc_pctr_final(SPC_CTR2_CTX *ctx) {
spc_memset(&ctx, 0, sizeof(SPC_CTR2_CTX));
return 1;
}
See Also
Recipes 5.5, 5.9, 13.2
Parallelizing Encryption and Decryption in Modes That Allow It (Without Breaking Compatibility) | 211
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