openssl - Converting PrivateKey to pem string without using bouncycastle

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openssl - Converting PrivateKey to pem string without using bouncycastle

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

openssl - Converting PrivateKey to pem string without using bouncycastle

I'm trying to convert a PrivateKey object to pem format string without using bouncycastle. previously I was doing it like this:

    StringWriter str = new StringWriter();
    PEMWriter pemWriter = new PEMWriter(str);
    pemWriter.writeObject(privKey);
    pemWriter.close();
    str.close();        
    return str.toString().getBytes();

Now I don't want to use bouncycastle. If I use

    String code = "-----BEGIN RSA PRIVATE KEY-----
";          
    String codenew =Base64.encodeBase64String(privKey.getEncoded());
    String myOutput = ""; 
    for (String substring : Splitter.fixedLength(64).split(codenew)) { 
      myOutput += substring + "
"; 
    }
    code += myOutput.substring(0, myOutput.length() - 1);
    code += "
-----END RSA PRIVATE KEY-----";                          
    return code.getBytes();

The code above works and I'm able to decrypt using openssl by passing this byte[]. Now, my problem is, if I'm printing the pem string value for the above two piece of code, they are different. If I'm using the below openssl command

$ openssl pkcs12 -in receiver.p12 -out receiver.pem -nodes

the pem string thats generated is same as PEMWriter's pem string but not the other one. I wanted to know can I modify my code a bit so that the string when printed, matches the one thats generated by openssl command or PEMWriter.

pem generated by openssl/PEMWriter:

pem generated when not using BC:

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1 Answer

深蓝 · Answer 1 · 2021-10-23T19:30:44+0000

PEMWriter class from BouncyCastle stores private key in PKCS#1 format (for more details please see RsaPrivateKey stucture defined in RFC 3447):

pkcs1

Your code stores private key in PKCS#8 format (for more details please see PrivateKeyInfo structure defined in RFC 5208):

pkcs8

PKCS#1 defines how to store RSA keys while PKCS#8 defines an envelope that can store any asymmetric key pair. As you can see on the attached pictures PKCS#8 just envelopes PKCS#1 and specifies that key is usable with RSA algorithm.

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openssl - Converting PrivateKey to pem string without using bouncycastle

openssl - Converting PrivateKey to pem string without using bouncycastle

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