proxmark3/client/amiitool/drbg.c

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/*
* (c) 2015-2017 Marcos Del Sol Vives
* (c) 2016 javiMaD
*
* SPDX-License-Identifier: MIT
*/
#include "drbg.h"
#include <assert.h>
#include <string.h>
#include <mbedtls/md.h>
void nfc3d_drbg_init(nfc3d_drbg_ctx * ctx, const uint8_t * hmacKey, size_t hmacKeySize, const uint8_t * seed, size_t seedSize) {
assert(ctx != NULL);
assert(hmacKey != NULL);
assert(seed != NULL);
assert(seedSize <= NFC3D_DRBG_MAX_SEED_SIZE);
// Initialize primitives
ctx->used = false;
ctx->iteration = 0;
ctx->bufferSize = sizeof(ctx->iteration) + seedSize;
// The 16-bit counter is prepended to the seed when hashing, so we'll leave 2 bytes at the start
memcpy(ctx->buffer + sizeof(uint16_t), seed, seedSize);
// Initialize underlying HMAC context
mbedtls_md_init(&ctx->hmacCtx);
mbedtls_md_setup(&ctx->hmacCtx, mbedtls_md_info_from_type(MBEDTLS_MD_SHA256), 1);
mbedtls_md_hmac_starts(&ctx->hmacCtx, hmacKey, hmacKeySize);
}
void nfc3d_drbg_step(nfc3d_drbg_ctx * ctx, uint8_t * output) {
assert(ctx != NULL);
assert(output != NULL);
if (ctx->used) {
// If used at least once, reinitialize the HMAC
mbedtls_md_hmac_reset(&ctx->hmacCtx);
} else {
ctx->used = true;
}
// Store counter in big endian, and increment it
ctx->buffer[0] = ctx->iteration >> 8;
ctx->buffer[1] = ctx->iteration >> 0;
ctx->iteration++;
// Do HMAC magic
mbedtls_md_hmac_update(&ctx->hmacCtx, ctx->buffer, ctx->bufferSize);
mbedtls_md_hmac_finish(&ctx->hmacCtx, output);
}
void nfc3d_drbg_cleanup(nfc3d_drbg_ctx * ctx) {
assert(ctx != NULL);
mbedtls_md_free(&ctx->hmacCtx);
}
void nfc3d_drbg_generate_bytes(const uint8_t * hmacKey, size_t hmacKeySize, const uint8_t * seed, size_t seedSize, uint8_t * output, size_t outputSize) {
uint8_t temp[NFC3D_DRBG_OUTPUT_SIZE];
nfc3d_drbg_ctx rngCtx;
nfc3d_drbg_init(&rngCtx, hmacKey, hmacKeySize, seed, seedSize);
while (outputSize > 0) {
if (outputSize < NFC3D_DRBG_OUTPUT_SIZE) {
nfc3d_drbg_step(&rngCtx, temp);
memcpy(output, temp, outputSize);
break;
}
nfc3d_drbg_step(&rngCtx, output);
output += NFC3D_DRBG_OUTPUT_SIZE;
outputSize -= NFC3D_DRBG_OUTPUT_SIZE;
}
nfc3d_drbg_cleanup(&rngCtx);
}