Add sanity check when loading public keys for OTA package
For RSA keys, check if it has a 2048 bits modulus, and its public
exponent is 3 or 65537. For EC keys, check if the field size is 256
bits for its curve.
Bug: 116655889
Test: unit tests pass
Change-Id: I5c00f4d2b61c98c434f0b49db232155d5d0770ec
diff --git a/verifier.cpp b/verifier.cpp
index 2101dcb..2dfc208 100644
--- a/verifier.cpp
+++ b/verifier.cpp
@@ -500,6 +500,48 @@
return result;
}
+bool CheckRSAKey(const std::unique_ptr<RSA, RSADeleter>& rsa) {
+ if (!rsa) {
+ return false;
+ }
+
+ const BIGNUM* out_n;
+ const BIGNUM* out_e;
+ RSA_get0_key(rsa.get(), &out_n, &out_e, nullptr /* private exponent */);
+ auto modulus_bits = BN_num_bits(out_n);
+ if (modulus_bits != 2048) {
+ LOG(ERROR) << "Modulus should be 2048 bits long, actual: " << modulus_bits;
+ return false;
+ }
+
+ BN_ULONG exponent = BN_get_word(out_e);
+ if (exponent != 3 && exponent != 65537) {
+ LOG(ERROR) << "Public exponent should be 3 or 65537, actual: " << exponent;
+ return false;
+ }
+
+ return true;
+}
+
+bool CheckECKey(const std::unique_ptr<EC_KEY, ECKEYDeleter>& ec_key) {
+ if (!ec_key) {
+ return false;
+ }
+
+ const EC_GROUP* ec_group = EC_KEY_get0_group(ec_key.get());
+ if (!ec_group) {
+ LOG(ERROR) << "Failed to get the ec_group from the ec_key";
+ return false;
+ }
+ auto degree = EC_GROUP_get_degree(ec_group);
+ if (degree != 256) {
+ LOG(ERROR) << "Field size of the ec key should be 256 bits long, actual: " << degree;
+ return false;
+ }
+
+ return true;
+}
+
bool LoadCertificateFromBuffer(const std::vector<uint8_t>& pem_content, Certificate* cert) {
std::unique_ptr<BIO, decltype(&BIO_free)> content(
BIO_new_mem_buf(pem_content.data(), pem_content.size()), BIO_free);
@@ -538,22 +580,20 @@
}
int key_type = EVP_PKEY_id(public_key.get());
- // TODO(xunchang) check the rsa key has exponent 3 or 65537 with RSA_get0_key; and ec key is
- // 256 bits.
if (key_type == EVP_PKEY_RSA) {
cert->key_type = Certificate::KEY_TYPE_RSA;
cert->ec.reset();
cert->rsa.reset(EVP_PKEY_get1_RSA(public_key.get()));
- if (!cert->rsa) {
- LOG(ERROR) << "Failed to get the rsa key info from public key";
+ if (!cert->rsa || !CheckRSAKey(cert->rsa)) {
+ LOG(ERROR) << "Failed to validate the rsa key info from public key";
return false;
}
} else if (key_type == EVP_PKEY_EC) {
cert->key_type = Certificate::KEY_TYPE_EC;
cert->rsa.reset();
cert->ec.reset(EVP_PKEY_get1_EC_KEY(public_key.get()));
- if (!cert->ec) {
- LOG(ERROR) << "Failed to get the ec key info from the public key";
+ if (!cert->ec || !CheckECKey(cert->ec)) {
+ LOG(ERROR) << "Failed to validate the ec key info from the public key";
return false;
}
} else {