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Add Tinycrypt based HKDF #702

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125 changes: 12 additions & 113 deletions boot/bootutil/src/encrypted.c
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Original file line number Diff line number Diff line change
Expand Up @@ -50,6 +50,7 @@
#include "tinycrypt/ecc_dh.h"
#include "tinycrypt/ctr_mode.h"
#include "tinycrypt/hmac.h"
#include "tinycrypt/hkdf.h"
#include "mbedtls/oid.h"
#include "mbedtls/asn1.h"
#endif
Expand Down Expand Up @@ -275,113 +276,6 @@ parse_ec256_enckey(uint8_t **p, uint8_t *end, uint8_t *pk)

return 0;
}

/*
* HKDF as described by RFC5869.
*
* @param ikm The input data to be derived.
* @param ikm_len Length of the input data.
* @param info An information tag.
* @param info_len Length of the information tag.
* @param okm Output of the KDF computation.
* @param okm_len On input the requested length; on output the generated length
*/
static int
hkdf(uint8_t *ikm, uint16_t ikm_len, uint8_t *info, uint16_t info_len,
uint8_t *okm, uint16_t *okm_len)
{
struct tc_hmac_state_struct hmac;
uint8_t salt[TC_SHA256_DIGEST_SIZE];
uint8_t prk[TC_SHA256_DIGEST_SIZE];
uint8_t T[TC_SHA256_DIGEST_SIZE];
uint16_t off;
uint16_t len;
uint8_t counter;
bool first;
int rc;

/*
* Extract
*/

if (ikm == NULL || okm == NULL || ikm_len == 0) {
return -1;
}

memset(salt, 0, TC_SHA256_DIGEST_SIZE);
rc = tc_hmac_set_key(&hmac, salt, TC_SHA256_DIGEST_SIZE);
if (rc != TC_CRYPTO_SUCCESS) {
return -1;
}

rc = tc_hmac_init(&hmac);
if (rc != TC_CRYPTO_SUCCESS) {
return -1;
}

rc = tc_hmac_update(&hmac, ikm, ikm_len);
if (rc != TC_CRYPTO_SUCCESS) {
return -1;
}

rc = tc_hmac_final(prk, TC_SHA256_DIGEST_SIZE, &hmac);
if (rc != TC_CRYPTO_SUCCESS) {
return -1;
}

/*
* Expand
*/

len = *okm_len;
counter = 1;
first = true;
for (off = 0; len > 0; off += TC_SHA256_DIGEST_SIZE, ++counter) {
rc = tc_hmac_set_key(&hmac, prk, TC_SHA256_DIGEST_SIZE);
if (rc != TC_CRYPTO_SUCCESS) {
return -1;
}

rc = tc_hmac_init(&hmac);
if (rc != TC_CRYPTO_SUCCESS) {
return -1;
}

if (first) {
first = false;
} else {
rc = tc_hmac_update(&hmac, T, TC_SHA256_DIGEST_SIZE);
if (rc != TC_CRYPTO_SUCCESS) {
return -1;
}
}

rc = tc_hmac_update(&hmac, info, info_len);
if (rc != TC_CRYPTO_SUCCESS) {
return -1;
}

rc = tc_hmac_update(&hmac, &counter, 1);
if (rc != TC_CRYPTO_SUCCESS) {
return -1;
}

rc = tc_hmac_final(T, TC_SHA256_DIGEST_SIZE, &hmac);
if (rc != TC_CRYPTO_SUCCESS) {
return -1;
}

if (len > TC_SHA256_DIGEST_SIZE) {
memcpy(&okm[off], T, TC_SHA256_DIGEST_SIZE);
len -= TC_SHA256_DIGEST_SIZE;
} else {
memcpy(&okm[off], T, len);
len = 0;
}
}

return 0;
}
#endif

int
Expand Down Expand Up @@ -445,12 +339,12 @@ boot_enc_decrypt(const uint8_t *buf, uint8_t *enckey)
struct tc_aes_key_sched_struct aes;
uint8_t tag[TC_SHA256_DIGEST_SIZE];
uint8_t shared[NUM_ECC_BYTES];
uint8_t prk[TC_SHA256_DIGEST_SIZE];
uint8_t derived_key[TC_AES_KEY_SIZE + TC_SHA256_DIGEST_SIZE];
uint8_t *cp;
uint8_t *cpend;
uint8_t pk[NUM_ECC_BYTES];
uint8_t counter[TC_AES_BLOCK_SIZE];
uint16_t len;
#endif
int rc = -1;

Expand Down Expand Up @@ -509,13 +403,18 @@ boot_enc_decrypt(const uint8_t *buf, uint8_t *enckey)
}

/*
* Expand shared secret to create keys for AES-128-CTR + HMAC-SHA256
* Use HKDF to expand shared secret to create keys for
* AES-128-CTR + HMAC-SHA256
*/

len = TC_AES_KEY_SIZE + TC_SHA256_DIGEST_SIZE;
rc = hkdf(shared, NUM_ECC_BYTES, (uint8_t *)"MCUBoot_ECIES_v1", 16,
derived_key, &len);
if (rc != 0 || len != (TC_AES_KEY_SIZE + TC_SHA256_DIGEST_SIZE)) {
rc = tc_hkdf_extract(shared, NUM_ECC_BYTES, NULL, 0, prk);
if (rc != TC_CRYPTO_SUCCESS) {
return -1;
}

rc = tc_hkdf_expand(prk, (uint8_t *)"MCUBoot_ECIES_v1", 16,
TC_AES_KEY_SIZE + TC_SHA256_DIGEST_SIZE, derived_key);
if (rc != TC_CRYPTO_SUCCESS) {
return -1;
}

Expand Down
1 change: 1 addition & 0 deletions boot/zephyr/CMakeLists.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -183,6 +183,7 @@ if(CONFIG_BOOT_ENCRYPT_EC256)
${TINYCRYPT_DIR}/source/aes_encrypt.c
${TINYCRYPT_DIR}/source/aes_decrypt.c
${TINYCRYPT_DIR}/source/ctr_mode.c
${TINYCRYPT_DIR}/source/hkdf.c
${TINYCRYPT_DIR}/source/hmac.c
${TINYCRYPT_DIR}/source/ecc_dh.c
)
Expand Down
1 change: 1 addition & 0 deletions sim/mcuboot-sys/build.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -210,6 +210,7 @@ fn main() {
conf.file("../../ext/tinycrypt/lib/source/aes_encrypt.c");
conf.file("../../ext/tinycrypt/lib/source/aes_decrypt.c");
conf.file("../../ext/tinycrypt/lib/source/ctr_mode.c");
conf.file("../../ext/tinycrypt/lib/source/hkdf.c");
conf.file("../../ext/tinycrypt/lib/source/hmac.c");
conf.file("../../ext/tinycrypt/lib/source/ecc_dh.c");
}
Expand Down