Creating RSA Public Key From String throws exception [duplicate]

Question

I've generated this test public key using open ssl command and I am trying to turn it into a public key using KeyFactory. It just keeps giving me an InvalidKeySpecException no matter what I try. Any advice at all would be appreciated.

private void prepKeys() {
    String AppKeyPub =
        "MIIFKzCCA5OgAwIBAgIUGRbwEi8QEl2q+5h9wQ8P5guIMuEwDQYJKoZIhvcNAQEL"
        + "BQAwgaQxCzAJBgNVBAYTAlNHMRIwEAYDVQQIDAlTaW5nYXBvcmUxEjAQBgNVBAcM"
        + "CVNpbmdhcG9yZTEVMBMGA1UECgwMVGVzdCBwdnQgbHRkMRMwEQYDVQQLDApUZXN0"
        + "dW5pdCAyMQ4wDAYDVQQDDAVUZXN0MjExMC8GCSqGSIb3DQEJARYidmFyYWxha3No"
        + "bWlfcnVwcGFfbmVAc2cuc21iYy5jby5qcDAeFw0yNDEyMTYwNzU3NTRaFw0yNTEy"
        + "MTEwNzU3NTRaMIGkMQswCQYDVQQGEwJTRzESMBAGA1UECAwJU2luZ2Fwb3JlMRIw"
        + "EAYDVQQHDAlTaW5nYXBvcmUxFTATBgNVBAoMDFRlc3QgcHZ0IGx0ZDETMBEGA1UE"
        + "CwwKVGVzdHVuaXQgMjEOMAwGA1UEAwwFVGVzdDIxMTAvBgkqhkiG9w0BCQEWInZh"
        + "cmFsYWtzaG1pX3J1cHBhX25lQHNnLnNtYmMuY28uanAwggGiMA0GCSqGSIb3DQEB"
        + "AQUAA4IBjwAwggGKAoIBgQCsuZJJqsD7ewKufNjRZVnL06bkAZIx1gD/erX4M4pS"
        + "2LsLp1o/7UbdffpWPpCSgzDB68LoJS8KZyKnJKrRYk41xIx23gXAxdC6siuHAQhg"
        + "sFiwi8ibwOvbVrO1zZWlDFHd8YQyBJAjTCETeeIgMiOzsOC88UJTzCYXmjzXflBC"
        + "8QMHRJStcR2WEsS8865nNHMpoR9J6ulE12DVV9Qt+oD7YgG9bKRHRNo72Ea+Cs2F"
        + "s6zXHS5Yrcqf+dh1LCCmHvTRhwBWBwXcEoJlg8bAeAooxTw5nL5t4myWYqqKIdJd"
        + "3x6MD+sa4J0PhGZPC78ztSPXCxRaHUGLUlKmZtd+y3xTCQoBRTMLrseXDRhd+RWD"
        + "cL5msCE9rQ7hTUZaa5t+hMLWjVXEAX5v53kupLRejQKwcCCGJlhWBSJ/lZUBAJ6K"
        + "i2WdRkYTrhTvFpWQz20+bUwf2dqKRSUElL4b/MdRLYyimxkIS/JLoygENCSxqAo6"
        + "Cuu+yWstRibeJvPEXXdQe0ECAwEAAaNTMFEwHQYDVR0OBBYEFMccKlW0OXXTDWAG"
        + "vMR1cjfDVh5HMB8GA1UdIwQYMBaAFMccKlW0OXXTDWAGvMR1cjfDVh5HMA8GA1Ud"
        + "EwEB/wQFMAMBAf8wDQYJKoZIhvcNAQELBQADggGBAGShQg0l1UnLuUV1m14j/v0c"
        + "umLcL3gpyGxsyBgCnC1LSxFgW8r/8E3V6VKNR+Ws6gm1oE+P8A2rh0V0+2IQqGli"
        + "eYgIUzjaqVF3aCw8dorPPy4kP9kr3ToPxy8dqe+kTHl/Y25RwUOzjVDRGpIJ7FnE"
        + "EBADtT+2m27T1wQZD3SAErK7Ix9HeUFvPHY1G3n/a3/3IQ3VY3hdWdUSvhzCA9mn"
        + "nfQBqGTuO5o7OQT+yQFge+81Fr1qeCicxAw4wLm5gfEVrG7tjKO1QhYkRGKEiqkw"
        + "j+7koa+DArl0KOIRSvjTpZuG0H6b72NAetQT6/95KovaTjAgwZ9ernCoH/mOD6DC"
        + "+eh052mO/VlowXkzHOwmfqODP4xWkX79T37eUScYccO6alqFhqJaE9CWT6bQDcXu"
        + "K9VS8WTu00cjgwZfa0gRmQn1Cbr4Q4JK04igp7OARCPMQuKDpIMjFAPQ+rev+X4T"
        + "+h6GQoYNpO0sqk7JS5fOhjKvKKvF/SBWAk0RI0P2dg==";

    // create the key factory
    try {
        KeyFactory kFactory = KeyFactory.getInstance("RSA");
        // decode base64 of your key
        byte[] decoded = Base64.getDecoder().decode(AppKeyPub);
        // generate the public key
        X509EncodedKeySpec spec = new X509EncodedKeySpec(decoded);
        PublicKey publicKey = (PublicKey) kFactory.generatePublic(spec);

        System.out.println("Public Key: " + publicKey);

    } catch (Exception e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
}

The OpenSSL commands below are used to generate keys:

# generate a private key with the correct length 
openssl genrsa -out private-key.pem 3072 
# generate corresponding public key 
openssl rsa -in private-key.pem -pubout -out public-key.pem 
# optional: create a self-signed certificate 
openssl req -new -x509 -key private-key.pem -out cert.pem -days 360

Could you edit your question and add what openssl commands you used to create test public key ? — Sridevi
– Sridevi, Commented Dec 17, 2024 at 7:01
This is not a key in X.509/SPKI format, but a certificate. If you want to extract the contained public key, first load the certificate with CertificateFactory#generateCertificate() and extract the key with X509Certificate#getPublic(). — Topaco
– Topaco, Commented Dec 17, 2024 at 7:26
@topaco i am storing the certificate in keyvault and get this string in my function app(java) for my further process. — Vara Lakshmi
– Vara Lakshmi, Commented Dec 17, 2024 at 7:33
generatecertificate() throws exception. InputStream inputStream = new ByteArrayInputStream(AppKeyPub .getBytes(StandardCharsets.UTF_8)); CertificateFactory fac = CertificateFactory.getInstance("X509"); X509Certificate encodedCert = (X509Certificate) fac.generateCertificate(inputStream); return (RSAPublicKey) encodedCert.getPublicKey(); — Vara Lakshmi
– Vara Lakshmi, Commented Dec 17, 2024 at 7:35

Sean Lin · Accepted Answer · 2024-12-17 10:03:04Z

1

I guess you copied the wrong key (maybe you wrongly copied the private key or the cert file). I use the your openssl commands to generate the public key (public-key.pem, the output file of the second command), then copy your code and change the public key to mine. The code works fine.

Normally public key would be shorter than the key you put in the code.

If you need to read public key from the cert. You can follow @Topaco's solution.

// create the cert factory
try {
    CertificateFactory certFactory = CertificateFactory.getInstance("X.509");
    // decode base64 of your key
    byte[] decoded = Base64.getDecoder().decode(AppKeyPub);
    Certificate cert = certFactory.generateCertificate(new ByteArrayInputStream(decoded));
    PublicKey publicKey = cert.getPublicKey();
    System.out.println("Public Key: " + publicKey);

} catch (Exception e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
}

edited Dec 17, 2024 at 10:03

answered Dec 17, 2024 at 7:34

Sean Lin

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4 Comments

Vara Lakshmi Dec 17, 2024 at 8:19

i have to upload the certificate to keyvault. i can not simply use the public-key from the second command as suggested.

Vara Lakshmi Dec 17, 2024 at 8:19

openssl genpkey -algorithm RSA -out rsa_key.pem -pkeyopt rsa_keygen_bits:2048 openssl req -new -key rsa_key.pem -out csr.pem openssl x509 -req -in csr.pem -signkey rsa_key.pem -out cert.pem -days 3650 copy cert.pem + rsa_key.pem combinedruk.pem

Vara Lakshmi Dec 17, 2024 at 8:20

the above commands will generate combined key pem file to upload it in kayvault. then i will read the file and use the public key as string in my function

Sean Lin Dec 17, 2024 at 10:04

@VaraLakshmi if you need to read public key from the cert, can follow Topaco's solution. I've tested and paste the code in my answer.

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