php：使用 RSA 私钥进行字符串加密（从 JAVA 转换为 php）

Question

I have this JAVA code & I need to write the same thing in php:

public static String signMsg(String msg, String privateKey)
throws Exception {
    byte[] bytes = Base64.getDecoder().decode(privateKey);
    PKCS8EncodedKeySpec spec = new PKCS8EncodedKeySpec(bytes);
    KeyFactory kf = KeyFactory.getInstance("RSA");
    Signature ps = Signature.getInstance("SHA256withRSA");
    ps.initSign(kf.generatePrivate(spec));
    ps.update(msg.getBytes("UTF-8"));
    byte[] sigBytes = ps.sign();
    return Base64.getEncoder().encodeToString(sigBytes);
}

• Any idea how to do that?

Thanks in advance:)

Answer 1

Regarding your first approach: A signature is created with the private key. The public key is used to verify the signature. Regarding your second approach: A HMAC is not the same as a signature.

The Java code loads a private key in PKCS8 format, PEM encoded without header and footer. In the PHP code the key can be read in the same format and encoding. Alternatively, the key can be loaded in PKCS#1 format. Regarding the encoding, a PEM or DER encoded key is also accepted.

Additionally, it must be specified which algorithm is used for signing. The Java code applies RSA with PKCS#1 v1.5 padding and SHA-256 as digest. Furthermore, the generated signature is Base64 encoded. In order for the PHP code to provide the same RSA signature, the same parameters must be used.

Note that signing does not necessarily generate the same signature using the same message and the same key. It depends on the algorithm. However, in the case of RSA with PKCS#1 v1.5 padding, always the same signature is generated (deterministic). For PSS, on the other hand, a different signature is generated each time (probabilistic).

The following PHP code uses the PHPSECLIB and generates the same signature as the Java code:

use phpseclib3\Crypt\RSA;

$privateKey= 'MIIEvg...';
   
$signatureB64 = base64_encode(                              // Base64 encode signature
    RSA::load($privateKey)->                                // Choose RSA, load private PKCS8 key
    withHash('sha256')->                                    // Choose SHA-256 as digest
    withPadding(RSA::SIGNATURE_PKCS1)->                     // Choose PKCS#1 v1.5 padding
    sign('The quick brown fox jumps over the lazy dog')     // Sign messsage
);

print($signatureB64);