Identity Credential: Add some support functions for mDL oem Hal. (4821cee9) · Commits · e / os / android_hardware_interfaces

identity/support/include/android/hardware/identity/support/IdentityCredentialSupport.h

+78 −0

Original line number	Diff line number	Diff line
		@@ -33,6 +33,7 @@ using ::std::optional;
		using ::std::string;
		using ::std::tuple;
		using ::std::vector;
		using ::std::pair;

		// ---------------------------------------------------------------------------
		// Miscellaneous utilities.
		@@ -119,6 +120,12 @@ optional<vector<uint8_t>> encryptAes128Gcm(const vector<uint8_t>& key, const vec
		optional<std::pair<vector<uint8_t>, vector<vector<uint8_t>>>> createEcKeyPairAndAttestation(
		const vector<uint8_t>& challenge, const vector<uint8_t>& applicationId);

		// Like createEcKeyPairAndAttestation() but allows you to choose the public key.
		//
		optional<vector<vector<uint8_t>>> createAttestationForEcPublicKey(
		const vector<uint8_t>& publicKey, const vector<uint8_t>& challenge,
		const vector<uint8_t>& applicationId);

		// Creates an 256-bit EC key using the NID_X9_62_prime256v1 curve, returns the
		// PKCS#8 encoded key-pair.
		//
		@@ -155,6 +162,12 @@ optional<vector<uint8_t>> ecKeyPairGetPkcs12(const vector<uint8_t>& keyPair, con
		//
		optional<vector<uint8_t>> signEcDsa(const vector<uint8_t>& key, const vector<uint8_t>& data);

		// Like signEcDsa() but instead of taking the data to be signed, takes a digest
		// of it instead.
		//
		optional<vector<uint8_t>> signEcDsaDigest(const vector<uint8_t>& key,
		const vector<uint8_t>& dataDigest);

		// Calculates the HMAC with SHA-256 for \|data\| using \|key\|. The calculated HMAC
		// is returned and will be 32 bytes.
		//
		@@ -175,6 +188,27 @@ bool checkEcDsaSignature(const vector<uint8_t>& digest, const vector<uint8_t>& s
		//
		optional<vector<uint8_t>> certificateChainGetTopMostKey(const vector<uint8_t>& certificateChain);

		// Extracts the public-key from the top-most certificate in \|certificateChain\|
		// (which should be a concatenated chain of DER-encoded X.509 certificates).
		//
		// Return offset and size of the public-key
		//
		optional<pair<size_t, size_t>> certificateFindPublicKey(const vector<uint8_t>& x509Certificate);

		// Extracts the TbsCertificate from the top-most certificate in \|certificateChain\|
		// (which should be a concatenated chain of DER-encoded X.509 certificates).
		//
		// Return offset and size of the TbsCertificate
		//
		optional<pair<size_t, size_t>> certificateTbsCertificate(const vector<uint8_t>& x509Certificate);

		// Extracts the Signature from the top-most certificate in \|certificateChain\|
		// (which should be a concatenated chain of DER-encoded X.509 certificates).
		//
		// Return offset and size of the Signature
		//
		optional<pair<size_t, size_t>> certificateFindSignature(const vector<uint8_t>& x509Certificate);

		// Generates a X.509 certificate for \|publicKey\| (which must be in the format
		// returned by ecKeyPairGetPublicKey()).
		//
		@@ -231,6 +265,11 @@ optional<vector<vector<uint8_t>>> certificateChainSplit(const vector<uint8_t>& c
		//
		bool certificateChainValidate(const vector<uint8_t>& certificateChain);

		// Returns true if \|certificate\| is signed by \|publicKey\|.
		//
		bool certificateSignedByPublicKey(const vector<uint8_t>& certificate,
		const vector<uint8_t>& publicKey);

		// Signs \|data\| and \|detachedContent\| with \|key\| (which must be in the format
		// returned by ecKeyPairGetPrivateKey()).
		//
		@@ -243,6 +282,21 @@ optional<vector<uint8_t>> coseSignEcDsa(const vector<uint8_t>& key, const vector
		const vector<uint8_t>& detachedContent,
		const vector<uint8_t>& certificateChain);

		// Creates a COSE_Signature1 where \|signatureToBeSigned\| is the ECDSA signature
		// of the ToBeSigned CBOR from RFC 8051 "4.4. Signing and Verification Process".
		//
		// The \|signatureToBeSigned\| is expected to be 64 bytes and contain the R value,
		// then the S value.
		//
		// The \|data\| parameter will be included in the COSE_Sign1 CBOR.
		//
		// If \|certificateChain\| is non-empty it's included in the 'x5chain'
		// protected header element (as as described in'draft-ietf-cose-x509-04').
		//
		optional<vector<uint8_t>> coseSignEcDsaWithSignature(const vector<uint8_t>& signatureToBeSigned,
		const vector<uint8_t>& data,
		const vector<uint8_t>& certificateChain);

		// Checks that \|signatureCoseSign1\| (in COSE_Sign1 format) is a valid signature
		// made with \|public_key\| (which must be in the format returned by
		// ecKeyPairGetPublicKey()) where \|detachedContent\| is the detached content.
		@@ -251,9 +305,23 @@ bool coseCheckEcDsaSignature(const vector<uint8_t>& signatureCoseSign1,
		const vector<uint8_t>& detachedContent,
		const vector<uint8_t>& publicKey);

		// Converts a DER-encoded signature to the format used in 'signature' bstr in COSE_Sign1.
		bool ecdsaSignatureDerToCose(const vector<uint8_t>& ecdsaDerSignature,
		vector<uint8_t>& ecdsaCoseSignature);

		// Converts from the format in in 'signature' bstr in COSE_Sign1 to DER encoding.
		bool ecdsaSignatureCoseToDer(const vector<uint8_t>& ecdsaCoseSignature,
		vector<uint8_t>& ecdsaDerSignature);

		// Extracts the payload from a COSE_Sign1.
		optional<vector<uint8_t>> coseSignGetPayload(const vector<uint8_t>& signatureCoseSign1);

		// Extracts the signature (of the ToBeSigned CBOR) from a COSE_Sign1.
		optional<vector<uint8_t>> coseSignGetSignature(const vector<uint8_t>& signatureCoseSign1);

		// Extracts the signature algorithm from a COSE_Sign1.
		optional<int> coseSignGetAlg(const vector<uint8_t>& signatureCoseSign1);

		// Extracts the X.509 certificate chain, if present. Returns the data as a
		// concatenated chain of DER-encoded X.509 certificates
		//
		@@ -269,6 +337,16 @@ optional<vector<uint8_t>> coseSignGetX5Chain(const vector<uint8_t>& signatureCos
		optional<vector<uint8_t>> coseMac0(const vector<uint8_t>& key, const vector<uint8_t>& data,
		const vector<uint8_t>& detachedContent);

		// Creates a COSE_Mac0 where \|digestToBeMaced\| is the HMAC-SHA256
		// of the ToBeMaced CBOR from RFC 8051 "6.3. How to Compute and Verify a MAC".
		//
		// The \|digestToBeMaced\| is expected to be 32 bytes.
		//
		// The \|data\| parameter will be included in the COSE_Mac0 CBOR.
		//
		optional<vector<uint8_t>> coseMacWithDigest(const vector<uint8_t>& digestToBeMaced,
		const vector<uint8_t>& data);

		// ---------------------------------------------------------------------------
		// Utility functions specific to IdentityCredential.
		// ---------------------------------------------------------------------------

identity/support/src/IdentityCredentialSupport.cpp

+362 −3

Original line number	Diff line number	Diff line
		@@ -24,6 +24,7 @@
		#include <stdarg.h>
		#include <stdio.h>
		#include <time.h>
		#include <chrono>
		#include <iomanip>

		#include <openssl/aes.h>
		@@ -684,6 +685,48 @@ static bool parseX509Certificates(const vector<uint8_t>& certificateChain,
		return true;
		}

		bool certificateSignedByPublicKey(const vector<uint8_t>& certificate,
		const vector<uint8_t>& publicKey) {
		const unsigned char* p = certificate.data();
		auto x509 = X509_Ptr(d2i_X509(nullptr, &p, certificate.size()));
		if (x509 == nullptr) {
		LOG(ERROR) << "Error parsing X509 certificate";
		return false;
		}

		auto group = EC_GROUP_Ptr(EC_GROUP_new_by_curve_name(NID_X9_62_prime256v1));
		auto point = EC_POINT_Ptr(EC_POINT_new(group.get()));
		if (EC_POINT_oct2point(group.get(), point.get(), publicKey.data(), publicKey.size(), nullptr) !=
		1) {
		LOG(ERROR) << "Error decoding publicKey";
		return false;
		}
		auto ecKey = EC_KEY_Ptr(EC_KEY_new());
		auto pkey = EVP_PKEY_Ptr(EVP_PKEY_new());
		if (ecKey.get() == nullptr \|\| pkey.get() == nullptr) {
		LOG(ERROR) << "Memory allocation failed";
		return false;
		}
		if (EC_KEY_set_group(ecKey.get(), group.get()) != 1) {
		LOG(ERROR) << "Error setting group";
		return false;
		}
		if (EC_KEY_set_public_key(ecKey.get(), point.get()) != 1) {
		LOG(ERROR) << "Error setting point";
		return false;
		}
		if (EVP_PKEY_set1_EC_KEY(pkey.get(), ecKey.get()) != 1) {
		LOG(ERROR) << "Error setting key";
		return false;
		}

		if (X509_verify(x509.get(), pkey.get()) != 1) {
		return false;
		}

		return true;
		}

		// TODO: Right now the only check we perform is to check that each certificate
		// is signed by its successor. We should - but currently don't - also check
		// things like valid dates etc.
		@@ -770,7 +813,8 @@ vector<uint8_t> sha256(const vector<uint8_t>& data) {
		return ret;
		}

		optional<vector<uint8_t>> signEcDsa(const vector<uint8_t>& key, const vector<uint8_t>& data) {
		optional<vector<uint8_t>> signEcDsaDigest(const vector<uint8_t>& key,
		const vector<uint8_t>& dataDigest) {
		auto bn = BIGNUM_Ptr(BN_bin2bn(key.data(), key.size(), nullptr));
		if (bn.get() == nullptr) {
		LOG(ERROR) << "Error creating BIGNUM";
		@@ -783,8 +827,7 @@ optional<vector<uint8_t>> signEcDsa(const vector<uint8_t>& key, const vector<uin
		return {};
		}

		auto digest = sha256(data);
		ECDSA_SIG* sig = ECDSA_do_sign(digest.data(), digest.size(), ec_key.get());
		ECDSA_SIG* sig = ECDSA_do_sign(dataDigest.data(), dataDigest.size(), ec_key.get());
		if (sig == nullptr) {
		LOG(ERROR) << "Error signing digest";
		return {};
		@@ -798,6 +841,10 @@ optional<vector<uint8_t>> signEcDsa(const vector<uint8_t>& key, const vector<uin
		return signature;
		}

		optional<vector<uint8_t>> signEcDsa(const vector<uint8_t>& key, const vector<uint8_t>& data) {
		return signEcDsaDigest(key, sha256(data));
		}

		optional<vector<uint8_t>> hmacSha256(const vector<uint8_t>& key, const vector<uint8_t>& data) {
		HMAC_CTX ctx;
		HMAC_CTX_init(&ctx);
		@@ -955,6 +1002,51 @@ optional<std::pair<vector<uint8_t>, vector<vector<uint8_t>>>> createEcKeyPairAnd
		return make_pair(keyPair, attestationCert.value());
		}

		optional<vector<vector<uint8_t>>> createAttestationForEcPublicKey(
		const vector<uint8_t>& publicKey, const vector<uint8_t>& challenge,
		const vector<uint8_t>& applicationId) {
		auto group = EC_GROUP_Ptr(EC_GROUP_new_by_curve_name(NID_X9_62_prime256v1));
		auto point = EC_POINT_Ptr(EC_POINT_new(group.get()));
		if (EC_POINT_oct2point(group.get(), point.get(), publicKey.data(), publicKey.size(), nullptr) !=
		1) {
		LOG(ERROR) << "Error decoding publicKey";
		return {};
		}
		auto ecKey = EC_KEY_Ptr(EC_KEY_new());
		auto pkey = EVP_PKEY_Ptr(EVP_PKEY_new());
		if (ecKey.get() == nullptr \|\| pkey.get() == nullptr) {
		LOG(ERROR) << "Memory allocation failed";
		return {};
		}
		if (EC_KEY_set_group(ecKey.get(), group.get()) != 1) {
		LOG(ERROR) << "Error setting group";
		return {};
		}
		if (EC_KEY_set_public_key(ecKey.get(), point.get()) != 1) {
		LOG(ERROR) << "Error setting point";
		return {};
		}
		if (EVP_PKEY_set1_EC_KEY(pkey.get(), ecKey.get()) != 1) {
		LOG(ERROR) << "Error setting key";
		return {};
		}

		uint64_t now = (std::chrono::duration_cast<std::chrono::nanoseconds>(
		std::chrono::system_clock::now().time_since_epoch()).
		count()/ 1000000000);
		uint64_t secondsInOneYear = 365 * 24 * 60 * 60;
		uint64_t expireTimeMs = (now + secondsInOneYear) * 1000;

		optional<vector<vector<uint8_t>>> attestationCert =
		createAttestation(pkey.get(), applicationId, challenge, now * 1000, expireTimeMs);
		if (!attestationCert) {
		LOG(ERROR) << "Error create attestation from key and challenge";
		return {};
		}

		return attestationCert.value();
		}

		optional<vector<uint8_t>> createEcKeyPair() {
		auto ec_key = EC_KEY_Ptr(EC_KEY_new());
		auto pkey = EVP_PKEY_Ptr(EVP_PKEY_new());
		@@ -1477,6 +1569,120 @@ optional<vector<uint8_t>> certificateChainGetTopMostKey(const vector<uint8_t>& c
		return publicKey;
		}

		optional<pair<size_t, size_t>> certificateFindPublicKey(const vector<uint8_t>& x509Certificate) {
		vector<X509_Ptr> certs;
		if (!parseX509Certificates(x509Certificate, certs)) {
		return {};
		}
		if (certs.size() < 1) {
		LOG(ERROR) << "No certificates in chain";
		return {};
		}

		auto pkey = EVP_PKEY_Ptr(X509_get_pubkey(certs[0].get()));
		if (pkey.get() == nullptr) {
		LOG(ERROR) << "No public key";
		return {};
		}

		auto ecKey = EC_KEY_Ptr(EVP_PKEY_get1_EC_KEY(pkey.get()));
		if (ecKey.get() == nullptr) {
		LOG(ERROR) << "Failed getting EC key";
		return {};
		}

		auto ecGroup = EC_KEY_get0_group(ecKey.get());
		auto ecPoint = EC_KEY_get0_public_key(ecKey.get());
		int size = EC_POINT_point2oct(ecGroup, ecPoint, POINT_CONVERSION_UNCOMPRESSED, nullptr, 0,
		nullptr);
		if (size == 0) {
		LOG(ERROR) << "Error generating public key encoding";
		return {};
		}
		vector<uint8_t> publicKey;
		publicKey.resize(size);
		EC_POINT_point2oct(ecGroup, ecPoint, POINT_CONVERSION_UNCOMPRESSED, publicKey.data(),
		publicKey.size(), nullptr);

		size_t publicKeyOffset = 0;
		size_t publicKeySize = (size_t)size;
		void* location = memmem((const void*)x509Certificate.data(), x509Certificate.size(),
		(const void*)publicKey.data(), publicKey.size());

		if (location == NULL) {
		LOG(ERROR) << "Error finding publicKey from x509Certificate";
		return {};
		}
		publicKeyOffset = (size_t)((const char)location - (const char)x509Certificate.data());

		return std::make_pair(publicKeyOffset, publicKeySize);
		}

		optional<pair<size_t, size_t>> certificateTbsCertificate(const vector<uint8_t>& x509Certificate) {
		vector<X509_Ptr> certs;
		if (!parseX509Certificates(x509Certificate, certs)) {
		return {};
		}
		if (certs.size() < 1) {
		LOG(ERROR) << "No certificates in chain";
		return {};
		}

		unsigned char* buf = NULL;
		int len = i2d_re_X509_tbs(certs[0].get(), &buf);
		if ((len < 0) \|\| (buf == NULL)) {
		LOG(ERROR) << "fail to extract tbsCertificate in x509Certificate";
		return {};
		}

		vector<uint8_t> tbsCertificate(len);
		memcpy(tbsCertificate.data(), buf, len);

		size_t tbsCertificateOffset = 0;
		size_t tbsCertificateSize = (size_t)len;
		void* location = memmem((const void*)x509Certificate.data(), x509Certificate.size(),
		(const void*)tbsCertificate.data(), tbsCertificate.size());

		if (location == NULL) {
		LOG(ERROR) << "Error finding tbsCertificate from x509Certificate";
		return {};
		}
		tbsCertificateOffset = (size_t)((const char)location - (const char)x509Certificate.data());

		return std::make_pair(tbsCertificateOffset, tbsCertificateSize);
		}

		optional<pair<size_t, size_t>> certificateFindSignature(const vector<uint8_t>& x509Certificate) {
		vector<X509_Ptr> certs;
		if (!parseX509Certificates(x509Certificate, certs)) {
		return {};
		}
		if (certs.size() < 1) {
		LOG(ERROR) << "No certificates in chain";
		return {};
		}

		ASN1_BIT_STRING* psig;
		X509_ALGOR* palg;
		X509_get0_signature((const ASN1_BIT_STRING)&psig, (const X509_ALGOR)&palg, certs[0].get());

		vector<char> signature(psig->length);
		memcpy(signature.data(), psig->data, psig->length);

		size_t signatureOffset = 0;
		size_t signatureSize = (size_t)psig->length;
		void* location = memmem((const void*)x509Certificate.data(), x509Certificate.size(),
		(const void*)signature.data(), signature.size());

		if (location == NULL) {
		LOG(ERROR) << "Error finding signature from x509Certificate";
		return {};
		}
		signatureOffset = (size_t)((const char)location - (const char)x509Certificate.data());

		return std::make_pair(signatureOffset, signatureSize);
		}

		// ---------------------------------------------------------------------------
		// COSE Utility Functions
		// ---------------------------------------------------------------------------
		@@ -1574,6 +1780,55 @@ bool ecdsaSignatureDerToCose(const vector<uint8_t>& ecdsaDerSignature,
		return true;
		}

		optional<vector<uint8_t>> coseSignEcDsaWithSignature(const vector<uint8_t>& signatureToBeSigned,
		const vector<uint8_t>& data,
		const vector<uint8_t>& certificateChain) {
		if (signatureToBeSigned.size() != 64) {
		LOG(ERROR) << "Invalid size for signatureToBeSigned, expected 64 got "
		<< signatureToBeSigned.size();
		return {};
		}

		cppbor::Map unprotectedHeaders;
		cppbor::Map protectedHeaders;

		protectedHeaders.add(COSE_LABEL_ALG, COSE_ALG_ECDSA_256);

		if (certificateChain.size() != 0) {
		optional<vector<vector<uint8_t>>> certs = support::certificateChainSplit(certificateChain);
		if (!certs) {
		LOG(ERROR) << "Error splitting certificate chain";
		return {};
		}
		if (certs.value().size() == 1) {
		unprotectedHeaders.add(COSE_LABEL_X5CHAIN, certs.value()[0]);
		} else {
		cppbor::Array certArray;
		for (const vector<uint8_t>& cert : certs.value()) {
		certArray.add(cert);
		}
		unprotectedHeaders.add(COSE_LABEL_X5CHAIN, std::move(certArray));
		}
		}

		vector<uint8_t> encodedProtectedHeaders = coseEncodeHeaders(protectedHeaders);

		cppbor::Array coseSign1;
		coseSign1.add(encodedProtectedHeaders);
		coseSign1.add(std::move(unprotectedHeaders));
		if (data.size() == 0) {
		cppbor::Null nullValue;
		coseSign1.add(std::move(nullValue));
		} else {
		coseSign1.add(data);
		}
		coseSign1.add(signatureToBeSigned);
		vector<uint8_t> signatureCoseSign1;
		signatureCoseSign1 = coseSign1.encode();

		return signatureCoseSign1;
		}

		optional<vector<uint8_t>> coseSignEcDsa(const vector<uint8_t>& key, const vector<uint8_t>& data,
		const vector<uint8_t>& detachedContent,
		const vector<uint8_t>& certificateChain) {
		@@ -1709,6 +1964,35 @@ bool coseCheckEcDsaSignature(const vector<uint8_t>& signatureCoseSign1,
		return true;
		}

		// Extracts the signature (of the ToBeSigned CBOR) from a COSE_Sign1.
		optional<vector<uint8_t>> coseSignGetSignature(const vector<uint8_t>& signatureCoseSign1) {
		auto [item, _, message] = cppbor::parse(signatureCoseSign1);
		if (item == nullptr) {
		LOG(ERROR) << "Passed-in COSE_Sign1 is not valid CBOR: " << message;
		return {};
		}
		const cppbor::Array* array = item->asArray();
		if (array == nullptr) {
		LOG(ERROR) << "Value for COSE_Sign1 is not an array";
		return {};
		}
		if (array->size() != 4) {
		LOG(ERROR) << "Value for COSE_Sign1 is not an array of size 4";
		return {};
		}

		vector<uint8_t> signature;
		const cppbor::Bstr* signatureAsBstr = (*array)[3]->asBstr();
		if (signatureAsBstr == nullptr) {
		LOG(ERROR) << "Value for signature is not a bstr";
		return {};
		}
		// Copy payload into \|data\|
		signature = signatureAsBstr->value();

		return signature;
		}

		optional<vector<uint8_t>> coseSignGetPayload(const vector<uint8_t>& signatureCoseSign1) {
		auto [item, _, message] = cppbor::parse(signatureCoseSign1);
		if (item == nullptr) {
		@@ -1746,6 +2030,59 @@ optional<vector<uint8_t>> coseSignGetPayload(const vector<uint8_t>& signatureCos
		return data;
		}

		optional<int> coseSignGetAlg(const vector<uint8_t>& signatureCoseSign1) {
		auto [item, _, message] = cppbor::parse(signatureCoseSign1);
		if (item == nullptr) {
		LOG(ERROR) << "Passed-in COSE_Sign1 is not valid CBOR: " << message;
		return {};
		}
		const cppbor::Array* array = item->asArray();
		if (array == nullptr) {
		LOG(ERROR) << "Value for COSE_Sign1 is not an array";
		return {};
		}
		if (array->size() != 4) {
		LOG(ERROR) << "Value for COSE_Sign1 is not an array of size 4";
		return {};
		}

		const cppbor::Bstr* protectedHeadersBytes = (*array)[0]->asBstr();
		if (protectedHeadersBytes == nullptr) {
		LOG(ERROR) << "Value for protectedHeaders is not a bstr";
		return {};
		}
		auto [item2, _2, message2] = cppbor::parse(protectedHeadersBytes->value());
		if (item2 == nullptr) {
		LOG(ERROR) << "Error parsing protectedHeaders: " << message2;
		return {};
		}
		const cppbor::Map* protectedHeaders = item2->asMap();
		if (protectedHeaders == nullptr) {
		LOG(ERROR) << "Decoded CBOR for protectedHeaders is not a map";
		return {};
		}

		for (size_t n = 0; n < protectedHeaders->size(); n++) {
		auto [keyItem, valueItem] = (*protectedHeaders)[n];
		const cppbor::Int* number = keyItem->asInt();
		if (number == nullptr) {
		LOG(ERROR) << "Key item in top-level map is not a number";
		return {};
		}
		int label = number->value();
		if (label == COSE_LABEL_ALG) {
		const cppbor::Int* number = valueItem->asInt();
		if (number != nullptr) {
		return number->value();
		}
		LOG(ERROR) << "Value for COSE_LABEL_ALG label is not a number";
		return {};
		}
		}
		LOG(ERROR) << "Did not find COSE_LABEL_ALG label in protected headers";
		return {};
		}

		optional<vector<uint8_t>> coseSignGetX5Chain(const vector<uint8_t>& signatureCoseSign1) {
		auto [item, _, message] = cppbor::parse(signatureCoseSign1);
		if (item == nullptr) {
		@@ -1861,6 +2198,28 @@ optional<vector<uint8_t>> coseMac0(const vector<uint8_t>& key, const vector<uint
		return array.encode();
		}

		optional<vector<uint8_t>> coseMacWithDigest(const vector<uint8_t>& digestToBeMaced,
		const vector<uint8_t>& data) {
		cppbor::Map unprotectedHeaders;
		cppbor::Map protectedHeaders;

		protectedHeaders.add(COSE_LABEL_ALG, COSE_ALG_HMAC_256_256);

		vector<uint8_t> encodedProtectedHeaders = coseEncodeHeaders(protectedHeaders);

		cppbor::Array array;
		array.add(encodedProtectedHeaders);
		array.add(std::move(unprotectedHeaders));
		if (data.size() == 0) {
		cppbor::Null nullValue;
		array.add(std::move(nullValue));
		} else {
		array.add(data);
		}
		array.add(digestToBeMaced);
		return array.encode();
		}

		// ---------------------------------------------------------------------------
		// Utility functions specific to IdentityCredential.
		// ---------------------------------------------------------------------------