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Add support for ECDSA signatures

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This adds support for key version 5 which is an EC key using the NIST
P-256 curve parameters. OTAs may be signed with these keys using the
ECDSA signature algorithm with SHA-256.

Change-Id: Id88672a3deb70681c78d5ea0d739e10f839e4567
This commit is contained in:
Kenny Root
2013-10-09 10:14:35 -07:00
parent 58c60900ac
commit 7a4adb5268
12 changed files with 823 additions and 61 deletions
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verifier.cpp
+198 -32
View File
@@ -14,10 +14,14 @@
* limitations under the License.
*/
#include "asn1_decoder.h"
#include "common.h"
#include "verifier.h"
#include "ui.h"
#include "verifier.h"
#include "mincrypt/dsa_sig.h"
#include "mincrypt/p256.h"
#include "mincrypt/p256_ecdsa.h"
#include "mincrypt/rsa.h"
#include "mincrypt/sha.h"
#include "mincrypt/sha256.h"
@@ -28,6 +32,78 @@
extern RecoveryUI* ui;
/*
* Simple version of PKCS#7 SignedData extraction. This extracts the
* signature OCTET STRING to be used for signature verification.
*
* For full details, see http://www.ietf.org/rfc/rfc3852.txt
*
* The PKCS#7 structure looks like:
*
* SEQUENCE (ContentInfo)
* OID (ContentType)
* [0] (content)
* SEQUENCE (SignedData)
* INTEGER (version CMSVersion)
* SET (DigestAlgorithmIdentifiers)
* SEQUENCE (EncapsulatedContentInfo)
* [0] (CertificateSet OPTIONAL)
* [1] (RevocationInfoChoices OPTIONAL)
* SET (SignerInfos)
* SEQUENCE (SignerInfo)
* INTEGER (CMSVersion)
* SEQUENCE (SignerIdentifier)
* SEQUENCE (DigestAlgorithmIdentifier)
* SEQUENCE (SignatureAlgorithmIdentifier)
* OCTET STRING (SignatureValue)
*/
static bool read_pkcs7(uint8_t* pkcs7_der, size_t pkcs7_der_len, uint8_t** sig_der,
size_t* sig_der_length) {
asn1_context_t* ctx = asn1_context_new(pkcs7_der, pkcs7_der_len);
if (ctx == NULL) {
return false;
}
asn1_context_t* pkcs7_seq = asn1_sequence_get(ctx);
if (pkcs7_seq != NULL && asn1_sequence_next(pkcs7_seq)) {
asn1_context_t *signed_data_app = asn1_constructed_get(pkcs7_seq);
if (signed_data_app != NULL) {
asn1_context_t* signed_data_seq = asn1_sequence_get(signed_data_app);
if (signed_data_seq != NULL
&& asn1_sequence_next(signed_data_seq)
&& asn1_sequence_next(signed_data_seq)
&& asn1_sequence_next(signed_data_seq)
&& asn1_constructed_skip_all(signed_data_seq)) {
asn1_context_t *sig_set = asn1_set_get(signed_data_seq);
if (sig_set != NULL) {
asn1_context_t* sig_seq = asn1_sequence_get(sig_set);
if (sig_seq != NULL
&& asn1_sequence_next(sig_seq)
&& asn1_sequence_next(sig_seq)
&& asn1_sequence_next(sig_seq)
&& asn1_sequence_next(sig_seq)) {
uint8_t* sig_der_ptr;
if (asn1_octet_string_get(sig_seq, &sig_der_ptr, sig_der_length)) {
*sig_der = (uint8_t*) malloc(*sig_der_length);
if (*sig_der != NULL) {
memcpy(*sig_der, sig_der_ptr, *sig_der_length);
}
}
asn1_context_free(sig_seq);
}
asn1_context_free(sig_set);
}
asn1_context_free(signed_data_seq);
}
asn1_context_free(signed_data_app);
}
asn1_context_free(pkcs7_seq);
}
asn1_context_free(ctx);
return *sig_der != NULL;
}
// Look for an RSA signature embedded in the .ZIP file comment given
// the path to the zip. Verify it matches one of the given public
// keys.
@@ -79,9 +155,8 @@ int verify_file(const char* path, const Certificate* pKeys, unsigned int numKeys
LOGI("comment is %d bytes; signature %d bytes from end\n",
comment_size, signature_start);
if (signature_start - FOOTER_SIZE < RSANUMBYTES) {
// "signature" block isn't big enough to contain an RSA block.
LOGE("signature is too short\n");
if (signature_start <= FOOTER_SIZE) {
LOGE("Signature start is in the footer");
fclose(f);
return VERIFY_FAILURE;
}
@@ -187,6 +262,23 @@ int verify_file(const char* path, const Certificate* pKeys, unsigned int numKeys
const uint8_t* sha1 = SHA_final(&sha1_ctx);
const uint8_t* sha256 = SHA256_final(&sha256_ctx);
uint8_t* sig_der = NULL;
size_t sig_der_length = 0;
size_t signature_size = signature_start - FOOTER_SIZE;
if (!read_pkcs7(eocd + eocd_size - signature_start, signature_size, &sig_der,
&sig_der_length)) {
LOGE("Could not find signature DER block\n");
free(eocd);
return VERIFY_FAILURE;
}
free(eocd);
/*
* Check to make sure at least one of the keys matches the signature. Since
* any key can match, we need to try each before determining a verification
* failure has happened.
*/
for (i = 0; i < numKeys; ++i) {
const uint8_t* hash;
switch (pKeys[i].hash_len) {
@@ -197,16 +289,46 @@ int verify_file(const char* path, const Certificate* pKeys, unsigned int numKeys
// The 6 bytes is the "(signature_start) $ff $ff (comment_size)" that
// the signing tool appends after the signature itself.
if (RSA_verify(pKeys[i].public_key, eocd + eocd_size - 6 - RSANUMBYTES,
RSANUMBYTES, hash, pKeys[i].hash_len)) {
LOGI("whole-file signature verified against key %d\n", i);
free(eocd);
if (pKeys[i].key_type == Certificate::RSA) {
if (sig_der_length < RSANUMBYTES) {
// "signature" block isn't big enough to contain an RSA block.
LOGI("signature is too short for RSA key %d\n", i);
continue;
}
if (!RSA_verify(pKeys[i].rsa, sig_der, RSANUMBYTES,
hash, pKeys[i].hash_len)) {
LOGI("failed to verify against RSA key %d\n", i);
continue;
}
LOGI("whole-file signature verified against RSA key %d\n", i);
free(sig_der);
return VERIFY_SUCCESS;
} else if (pKeys[i].key_type == Certificate::EC
&& pKeys[i].hash_len == SHA256_DIGEST_SIZE) {
p256_int r, s;
if (!dsa_sig_unpack(sig_der, sig_der_length, &r, &s)) {
LOGI("Not a DSA signature block for EC key %d\n", i);
continue;
}
p256_int p256_hash;
p256_from_bin(hash, &p256_hash);
if (!p256_ecdsa_verify(&(pKeys[i].ec->x), &(pKeys[i].ec->y),
&p256_hash, &r, &s)) {
LOGI("failed to verify against EC key %d\n", i);
continue;
}
LOGI("whole-file signature verified against EC key %d\n", i);
free(sig_der);
return VERIFY_SUCCESS;
} else {
LOGI("failed to verify against key %d\n", i);
LOGI("Unknown key type %d\n", pKeys[i].key_type);
}
}
free(eocd);
free(sig_der);
LOGE("failed to verify whole-file signature\n");
return VERIFY_FAILURE;
}
@@ -238,6 +360,7 @@ int verify_file(const char* path, const Certificate* pKeys, unsigned int numKeys
// 2: 2048-bit RSA key with e=65537 and SHA-1 hash
// 3: 2048-bit RSA key with e=3 and SHA-256 hash
// 4: 2048-bit RSA key with e=65537 and SHA-256 hash
// 5: 256-bit EC key using the NIST P-256 curve parameters and SHA-256 hash
//
// Returns NULL if the file failed to parse, or if it contain zero keys.
Certificate*
@@ -258,28 +381,41 @@ load_keys(const char* filename, int* numKeys) {
++*numKeys;
out = (Certificate*)realloc(out, *numKeys * sizeof(Certificate));
Certificate* cert = out + (*numKeys - 1);
cert->public_key = (RSAPublicKey*)malloc(sizeof(RSAPublicKey));
memset(cert, '\0', sizeof(Certificate));
char start_char;
if (fscanf(f, " %c", &start_char) != 1) goto exit;
if (start_char == '{') {
// a version 1 key has no version specifier.
cert->public_key->exponent = 3;
cert->key_type = Certificate::RSA;
cert->rsa = (RSAPublicKey*)malloc(sizeof(RSAPublicKey));
cert->rsa->exponent = 3;
cert->hash_len = SHA_DIGEST_SIZE;
} else if (start_char == 'v') {
int version;
if (fscanf(f, "%d {", &version) != 1) goto exit;
switch (version) {
case 2:
cert->public_key->exponent = 65537;
cert->key_type = Certificate::RSA;
cert->rsa = (RSAPublicKey*)malloc(sizeof(RSAPublicKey));
cert->rsa->exponent = 65537;
cert->hash_len = SHA_DIGEST_SIZE;
break;
case 3:
cert->public_key->exponent = 3;
cert->key_type = Certificate::RSA;
cert->rsa = (RSAPublicKey*)malloc(sizeof(RSAPublicKey));
cert->rsa->exponent = 3;
cert->hash_len = SHA256_DIGEST_SIZE;
break;
case 4:
cert->public_key->exponent = 65537;
cert->key_type = Certificate::RSA;
cert->rsa = (RSAPublicKey*)malloc(sizeof(RSAPublicKey));
cert->rsa->exponent = 65537;
cert->hash_len = SHA256_DIGEST_SIZE;
break;
case 5:
cert->key_type = Certificate::EC;
cert->ec = (ECPublicKey*)calloc(1, sizeof(ECPublicKey));
cert->hash_len = SHA256_DIGEST_SIZE;
break;
default:
@@ -287,23 +423,55 @@ load_keys(const char* filename, int* numKeys) {
}
}
RSAPublicKey* key = cert->public_key;
if (fscanf(f, " %i , 0x%x , { %u",
&(key->len), &(key->n0inv), &(key->n[0])) != 3) {
if (cert->key_type == Certificate::RSA) {
RSAPublicKey* key = cert->rsa;
if (fscanf(f, " %i , 0x%x , { %u",
&(key->len), &(key->n0inv), &(key->n[0])) != 3) {
goto exit;
}
if (key->len != RSANUMWORDS) {
LOGE("key length (%d) does not match expected size\n", key->len);
goto exit;
}
for (i = 1; i < key->len; ++i) {
if (fscanf(f, " , %u", &(key->n[i])) != 1) goto exit;
}
if (fscanf(f, " } , { %u", &(key->rr[0])) != 1) goto exit;
for (i = 1; i < key->len; ++i) {
if (fscanf(f, " , %u", &(key->rr[i])) != 1) goto exit;
}
fscanf(f, " } } ");
LOGI("read key e=%d hash=%d\n", key->exponent, cert->hash_len);
} else if (cert->key_type == Certificate::EC) {
ECPublicKey* key = cert->ec;
int key_len;
unsigned int byte;
uint8_t x_bytes[P256_NBYTES];
uint8_t y_bytes[P256_NBYTES];
if (fscanf(f, " %i , { %u", &key_len, &byte) != 2) goto exit;
if (key_len != P256_NBYTES) {
LOGE("Key length (%d) does not match expected size %d\n", key_len, P256_NBYTES);
goto exit;
}
x_bytes[P256_NBYTES - 1] = byte;
for (i = P256_NBYTES - 2; i >= 0; --i) {
if (fscanf(f, " , %u", &byte) != 1) goto exit;
x_bytes[i] = byte;
}
if (fscanf(f, " } , { %u", &byte) != 1) goto exit;
y_bytes[P256_NBYTES - 1] = byte;
for (i = P256_NBYTES - 2; i >= 0; --i) {
if (fscanf(f, " , %u", &byte) != 1) goto exit;
y_bytes[i] = byte;
}
fscanf(f, " } } ");
p256_from_bin(x_bytes, &key->x);
p256_from_bin(y_bytes, &key->y);
} else {
LOGE("Unknown key type %d\n", cert->key_type);
goto exit;
}
if (key->len != RSANUMWORDS) {
LOGE("key length (%d) does not match expected size\n", key->len);
goto exit;
}
for (i = 1; i < key->len; ++i) {
if (fscanf(f, " , %u", &(key->n[i])) != 1) goto exit;
}
if (fscanf(f, " } , { %u", &(key->rr[0])) != 1) goto exit;
for (i = 1; i < key->len; ++i) {
if (fscanf(f, " , %u", &(key->rr[i])) != 1) goto exit;
}
fscanf(f, " } } ");
// if the line ends in a comma, this file has more keys.
switch (fgetc(f)) {
@@ -319,8 +487,6 @@ load_keys(const char* filename, int* numKeys) {
LOGE("unexpected character between keys\n");
goto exit;
}
LOGI("read key e=%d hash=%d\n", key->exponent, cert->hash_len);
}
}