Add support for ECDSA signatures
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
diff --git a/verifier.cpp b/verifier.cpp
index 782a838..0930fbd 100644
--- a/verifier.cpp
+++ b/verifier.cpp
@@ -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 @@
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 @@
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 @@
// 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 @@
// 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 @@
++*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 @@
}
}
- 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 @@
LOGE("unexpected character between keys\n");
goto exit;
}
-
- LOGI("read key e=%d hash=%d\n", key->exponent, cert->hash_len);
}
}