如何解析 x509 证书并提取其密钥的签名算法？

Question

我有一个 x509 证书作为 file/byte 数组，我想用它来验证 CertificateVerify TLS 消息中提供的签名。我想我可以使用 SecKeyVerifySignature once I've determined the certificate's key algorithm (SecKeyAlgorithm parameter) and initialized the signedData from the transcript hash（连接到上下文字符串等）。

openssl x509 报告证书的密钥，如

Subject Public Key Info:
    Public Key Algorithm: id-ecPublicKey
        Public-Key: (256 bit)
        pub:
            04:44:58:8c:d0:95:90:14:45:82:db:4f:56:41:7d:
            57:0e:f5:b4:d8:65:04:6c:21:5a:cd:1e:0e:87:10:
            f9:31:c6:fa:b9:ad:b3:a5:e1:df:9f:32:25:4b:a9:
            40:5c:d4:56:0d:bb:55:fd:f4:68:f9:4e:89:70:56:
            b9:1c:4a:ef:93
        ASN1 OID: prime256v1
        NIST CURVE: P-256

我相信我可以用 here 描述的机制解析证书，例如

CFDataRef certData = CFDataCreate(NULL, (const UInt8*) rawCert, len);
SecCertificateRef certificate = SecCertificateCreateWithData(NULL, certData);

而且我想我可以使用 SecCertificateCopyKey 来提取密钥，例如

SecKeyRef key = SecCertificateCopyKey(certificate);

但是，我找不到提取密钥签名算法（Public 密钥算法）的方法。我找到了 SecKeyIsAlgorithmSupported。我是否需要遍历所有可能的 SecKeyAlgorithm 常量以找到密钥正在使用的常量（即 id-ecPublicKey 的 SecKeyAlgorithm）？

Answer 1

我误解了自己的目标。

CertificateVerify 消息提供了到此为止的握手摘要。服务器使用其证书的私钥来执行该签名。如the TLS 1.3 specification所示，签名算法是CertificateVerify结构的一部分

struct {
    SignatureScheme algorithm;
    opaque signature<0..2^16-1>;
} CertificateVerify;

我只需要提取它并将其转换为 SecKeyAlgorithm。例如（使用 C++）

SecKeyAlgorithm keyAlgorithm;
// algorithm extracted from CertificateVerify
switch (algorithm) {
  case SignatureScheme::ecdsa_secp256r1_sha256:
    keyAlgorithm = kSecKeyAlgorithmECDSASignatureDigestX962SHA256;
    break;
  case SignatureScheme::rsa_pss_sha256:
    keyAlgorithm = kSecKeyAlgorithmRSASignatureDigestPSSSHA256;
    break;
  case SignatureScheme::ed25519:
  case SignatureScheme::ed448:
  default:
    throw std::runtime_error("unsupported peer cert type");
}

然后我可以确认证书支持该算法

if (!SecKeyIsAlgorithmSupported(key, kSecKeyOperationTypeVerify, keyAlgorithm)) {
  CFRelease(publicKey);
  throw std::runtime_error("Unsupported signature scheme");
}

最后用CertificateVerify中的signature和握手编译后的签名数据进行验证

CFErrorRef error;
bool signatureVerified = SecKeyVerifySignature(key, keyAlgorithm, toBeSignedData, signature, &error);
if (!signatureVerified) {
  CFRelease(error); // or use it
  throw std::runtime_error("Signature verification failed");
}

如何解析 x509 证书并提取其密钥的签名算法？

How do I parse an x509 certificate and extract its key's signature algorithm?

ssl

security-framework

x509certificate

ios

tls1.3