Support signing payload with 4096 bits RSA keys
The 32 bytes sha256 hash was padded to 256 bytes before payload signing
and verification. During the padding, we appended a hard coded header
according to RFC3447 spec.
As we want to support signing with 4096 bits keys, the format of the
padding doesn't change but the length needs adjustion. Now callers will
pass in the RSA size in bytes in the padding function. And the
verification function will now take the raw 32 bytes sha256 hash instead
of the padded value.
The new key for unittest is generated by:
openssl genrsa -out unittest_key_RSA4096.pem 4096
Bug: 129163830
Test: unit tests pass, create and install an update signed by 4096 bits key.
Change-Id: I8e0d02ddb1472e22976c0f170e8bf2b8b094c7d4
diff --git a/payload_consumer/delta_performer.cc b/payload_consumer/delta_performer.cc
index ae73d03..d76a959 100644
--- a/payload_consumer/delta_performer.cc
+++ b/payload_consumer/delta_performer.cc
@@ -1816,9 +1816,7 @@
!signatures_message_data_.empty());
brillo::Blob hash_data = signed_hash_calculator_.raw_hash();
TEST_AND_RETURN_VAL(ErrorCode::kDownloadPayloadPubKeyVerificationError,
- PayloadVerifier::PadRSA2048SHA256Hash(&hash_data));
- TEST_AND_RETURN_VAL(ErrorCode::kDownloadPayloadPubKeyVerificationError,
- !hash_data.empty());
+ hash_data.size() == kSHA256Size);
if (!PayloadVerifier::VerifySignature(
signatures_message_data_, public_key, hash_data)) {
diff --git a/payload_consumer/payload_metadata.cc b/payload_consumer/payload_metadata.cc
index 8b3eb4e..3739767 100644
--- a/payload_consumer/payload_metadata.cc
+++ b/payload_consumer/payload_metadata.cc
@@ -20,6 +20,7 @@
#include <brillo/data_encoding.h>
+#include "update_engine/common/constants.h"
#include "update_engine/common/hash_calculator.h"
#include "update_engine/common/utils.h"
#include "update_engine/payload_consumer/payload_constants.h"
@@ -187,16 +188,16 @@
return ErrorCode::kDownloadMetadataSignatureMissingError;
}
- brillo::Blob calculated_metadata_hash;
+ brillo::Blob metadata_hash;
if (!HashCalculator::RawHashOfBytes(
- payload.data(), metadata_size_, &calculated_metadata_hash)) {
+ payload.data(), metadata_size_, &metadata_hash)) {
LOG(ERROR) << "Unable to compute actual hash of manifest";
return ErrorCode::kDownloadMetadataSignatureVerificationError;
}
- PayloadVerifier::PadRSA2048SHA256Hash(&calculated_metadata_hash);
- if (calculated_metadata_hash.empty()) {
- LOG(ERROR) << "Computed actual hash of metadata is empty.";
+ if (metadata_hash.size() != kSHA256Size) {
+ LOG(ERROR) << "Computed actual hash of metadata has incorrect size: "
+ << metadata_hash.size();
return ErrorCode::kDownloadMetadataSignatureVerificationError;
}
@@ -207,17 +208,25 @@
LOG(ERROR) << "Unable to compute expected hash from metadata signature";
return ErrorCode::kDownloadMetadataSignatureError;
}
- if (calculated_metadata_hash != expected_metadata_hash) {
+
+ brillo::Blob padded_metadata_hash = metadata_hash;
+ if (!PayloadVerifier::PadRSASHA256Hash(&padded_metadata_hash,
+ expected_metadata_hash.size())) {
+ LOG(ERROR) << "Failed to pad the SHA256 hash to "
+ << expected_metadata_hash.size() << " bytes.";
+ return ErrorCode::kDownloadMetadataSignatureVerificationError;
+ }
+
+ if (padded_metadata_hash != expected_metadata_hash) {
LOG(ERROR) << "Manifest hash verification failed. Expected hash = ";
utils::HexDumpVector(expected_metadata_hash);
LOG(ERROR) << "Calculated hash = ";
- utils::HexDumpVector(calculated_metadata_hash);
+ utils::HexDumpVector(padded_metadata_hash);
return ErrorCode::kDownloadMetadataSignatureMismatch;
}
} else {
- if (!PayloadVerifier::VerifySignature(metadata_signature_protobuf,
- pem_public_key,
- calculated_metadata_hash)) {
+ if (!PayloadVerifier::VerifySignature(
+ metadata_signature_protobuf, pem_public_key, metadata_hash)) {
LOG(ERROR) << "Manifest hash verification failed.";
return ErrorCode::kDownloadMetadataSignatureMismatch;
}
diff --git a/payload_consumer/payload_verifier.cc b/payload_consumer/payload_verifier.cc
index 3eb1da8..3a3ccbf 100644
--- a/payload_consumer/payload_verifier.cc
+++ b/payload_consumer/payload_verifier.cc
@@ -16,11 +16,13 @@
#include "update_engine/payload_consumer/payload_verifier.h"
+#include <utility>
#include <vector>
#include <base/logging.h>
#include <openssl/pem.h>
+#include "update_engine/common/constants.h"
#include "update_engine/common/hash_calculator.h"
#include "update_engine/common/utils.h"
#include "update_engine/update_metadata.pb.h"
@@ -31,57 +33,27 @@
namespace {
-// The following is a standard PKCS1-v1_5 padding for SHA256 signatures, as
-// defined in RFC3447. It is prepended to the actual signature (32 bytes) to
-// form a sequence of 256 bytes (2048 bits) that is amenable to RSA signing. The
-// padded hash will look as follows:
+// The ASN.1 DigestInfo prefix for encoding SHA256 digest. The complete 51-byte
+// DigestInfo consists of 19-byte SHA256_DIGEST_INFO_PREFIX and 32-byte SHA256
+// digest.
//
-// 0x00 0x01 0xff ... 0xff 0x00 ASN1HEADER SHA256HASH
-// |--------------205-----------||----19----||----32----|
-//
-// where ASN1HEADER is the ASN.1 description of the signed data. The complete 51
-// bytes of actual data (i.e. the ASN.1 header complete with the hash) are
-// packed as follows:
-//
-// SEQUENCE(2+49) {
+// SEQUENCE(2+49) {
// SEQUENCE(2+13) {
-// OBJECT(2+9) id-sha256
-// NULL(2+0)
+// OBJECT(2+9) id-sha256
+// NULL(2+0)
// }
// OCTET STRING(2+32) <actual signature bytes...>
-// }
-// clang-format off
-const uint8_t kRSA2048SHA256Padding[] = {
- // PKCS1-v1_5 padding
- 0x00, 0x01, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
- 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
- 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
- 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
- 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
- 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
- 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
- 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
- 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
- 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
- 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
- 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
- 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
- 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
- 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
- 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
- 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
- 0x00,
- // ASN.1 header
- 0x30, 0x31, 0x30, 0x0d, 0x06, 0x09, 0x60, 0x86, 0x48, 0x01, 0x65, 0x03,
- 0x04, 0x02, 0x01, 0x05, 0x00, 0x04, 0x20,
+// }
+const uint8_t kSHA256DigestInfoPrefix[] = {
+ 0x30, 0x31, 0x30, 0x0d, 0x06, 0x09, 0x60, 0x86, 0x48, 0x01,
+ 0x65, 0x03, 0x04, 0x02, 0x01, 0x05, 0x00, 0x04, 0x20,
};
-// clang-format on
} // namespace
bool PayloadVerifier::VerifySignature(const string& signature_proto,
const string& pem_public_key,
- const brillo::Blob& hash_data) {
+ const brillo::Blob& sha256_hash_data) {
Signatures signatures;
LOG(INFO) << "signature blob size = " << signature_proto.size();
TEST_AND_RETURN_FALSE(signatures.ParseFromString(signature_proto));
@@ -100,7 +72,9 @@
if (!GetRawHashFromSignature(sig_data, pem_public_key, &sig_hash_data))
continue;
- if (hash_data == sig_hash_data) {
+ brillo::Blob padded_hash_data = sha256_hash_data;
+ if (PadRSASHA256Hash(&padded_hash_data, sig_hash_data.size()) &&
+ padded_hash_data == sig_hash_data) {
LOG(INFO) << "Verified correct signature " << i + 1 << " out of "
<< signatures.signatures_size() << " signatures.";
return true;
@@ -108,8 +82,8 @@
tested_hashes.push_back(sig_hash_data);
}
LOG(ERROR) << "None of the " << signatures.signatures_size()
- << " signatures is correct. Expected:";
- utils::HexDumpVector(hash_data);
+ << " signatures is correct. Expected hash before padding:";
+ utils::HexDumpVector(sha256_hash_data);
LOG(ERROR) << "But found decrypted hashes:";
for (const auto& sig_hash_data : tested_hashes) {
utils::HexDumpVector(sig_hash_data);
@@ -150,13 +124,30 @@
return true;
}
-bool PayloadVerifier::PadRSA2048SHA256Hash(brillo::Blob* hash) {
- TEST_AND_RETURN_FALSE(hash->size() == 32);
- hash->insert(hash->begin(),
- reinterpret_cast<const char*>(kRSA2048SHA256Padding),
- reinterpret_cast<const char*>(kRSA2048SHA256Padding +
- sizeof(kRSA2048SHA256Padding)));
- TEST_AND_RETURN_FALSE(hash->size() == 256);
+bool PayloadVerifier::PadRSASHA256Hash(brillo::Blob* hash, size_t rsa_size) {
+ TEST_AND_RETURN_FALSE(hash->size() == kSHA256Size);
+ TEST_AND_RETURN_FALSE(rsa_size == 256 || rsa_size == 512);
+
+ // The following is a standard PKCS1-v1_5 padding for SHA256 signatures, as
+ // defined in RFC3447 section 9.2. It is prepended to the actual signature
+ // (32 bytes) to form a sequence of 256|512 bytes (2048|4096 bits) that is
+ // amenable to RSA signing. The padded hash will look as follows:
+ //
+ // 0x00 0x01 0xff ... 0xff 0x00 ASN1HEADER SHA256HASH
+ // |-----------205|461----------||----19----||----32----|
+ size_t padding_string_size =
+ rsa_size - hash->size() - sizeof(kSHA256DigestInfoPrefix) - 3;
+ brillo::Blob padded_result = brillo::CombineBlobs({
+ {0x00, 0x01},
+ brillo::Blob(padding_string_size, 0xff),
+ {0x00},
+ brillo::Blob(kSHA256DigestInfoPrefix,
+ kSHA256DigestInfoPrefix + sizeof(kSHA256DigestInfoPrefix)),
+ *hash,
+ });
+
+ *hash = std::move(padded_result);
+ TEST_AND_RETURN_FALSE(hash->size() == rsa_size);
return true;
}
diff --git a/payload_consumer/payload_verifier.h b/payload_consumer/payload_verifier.h
index 09bdbf9..af8e05f 100644
--- a/payload_consumer/payload_verifier.h
+++ b/payload_consumer/payload_verifier.h
@@ -34,12 +34,13 @@
// Interprets |signature_proto| as a protocol buffer containing the Signatures
// message and decrypts each signature data using the |pem_public_key|.
// |pem_public_key| should be a PEM format RSA public key data.
- // Returns whether *any* of the decrypted hashes matches the |hash_data|.
- // In case of any error parsing the signatures or the public key, returns
- // false.
+ // Pads the 32 bytes |sha256_hash_data| to 256 or 512 bytes according to the
+ // PKCS#1 v1.5 standard; and returns whether *any* of the decrypted hashes
+ // matches the padded hash data. In case of any error parsing the signatures
+ // or the public key, returns false.
static bool VerifySignature(const std::string& signature_proto,
const std::string& pem_public_key,
- const brillo::Blob& hash_data);
+ const brillo::Blob& sha256_hash_data);
// Decrypts |sig_data| with the given |pem_public_key| and populates
// |out_hash_data| with the decoded raw hash. |pem_public_key| should be a PEM
@@ -48,12 +49,13 @@
const std::string& pem_public_key,
brillo::Blob* out_hash_data);
- // Pads a SHA256 hash so that it may be encrypted/signed with RSA2048
- // using the PKCS#1 v1.5 scheme.
- // hash should be a pointer to vector of exactly 256 bits. The vector
- // will be modified in place and will result in having a length of
- // 2048 bits. Returns true on success, false otherwise.
- static bool PadRSA2048SHA256Hash(brillo::Blob* hash);
+ // Pads a SHA256 hash so that it may be encrypted/signed with RSA2048 or
+ // RSA4096 using the PKCS#1 v1.5 scheme.
+ // hash should be a pointer to vector of exactly 256 bits. |rsa_size| must be
+ // one of 256 or 512 bytes. The vector will be modified in place and will
+ // result in having a length of 2048 or 4096 bits, depending on the rsa size.
+ // Returns true on success, false otherwise.
+ static bool PadRSASHA256Hash(brillo::Blob* hash, size_t rsa_size);
private:
// This should never be constructed