原文地址：https://stackoverflow.com/questions/7611383/generating-rsa-keys-in-pkcs1-format-in-java

When I generate an RSA key pair using the Java API, the public key is encoded in the X.509 format and the private key is encoded in the PKCS#8 format. I'm looking to encode both as PKCS#1. Is this possible? I've spent a considerable amount of time going through the Java docs but haven't found a solution. The result is the same when I use the Java and the Bouncy Castle providers.

Here is a snippet of the code:

KeyPairGeneratorkeygen=KeyPairGenerator.getInstance("RSA","BC");keygen.initialize(1024);KeyPairpair=keygen.generateKeyPair();PrivateKeypriv=pair.getPrivate();PublicKeypub=pair.getPublic();byte[]privBytes=priv.getEncoded();byte[]pubBytes=pub.getEncoded();

The two resulting byte arrays are formatted as X.509 (public) and PKCS#8 (private).

Any help would be much appreciated. There are some similar posts but none really answer my question.

Thank You

You will need BouncyCastle:

importorg.bouncycastle.asn1.ASN1Encodable;importorg.bouncycastle.asn1.ASN1Primitive;importorg.bouncycastle.asn1.pkcs.PrivateKeyInfo;importorg.bouncycastle.asn1.x509.SubjectPublicKeyInfo;importorg.bouncycastle.util.io.pem.PemObject;importorg.bouncycastle.util.io.pem.PemWriter;

The code snippets below have been checked and found working with Bouncy Castle 1.52.

Private key

Convert private key from PKCS8 to PKCS1:

PrivateKeypriv=pair.getPrivate();byte[]privBytes=priv.getEncoded();PrivateKeyInfopkInfo=PrivateKeyInfo.getInstance(privBytes);ASN1Encodable encodable=pkInfo.parsePrivateKey();ASN1Primitive primitive=encodable.toASN1Primitive();byte[]privateKeyPKCS1=primitive.getEncoded();

Convert private key in PKCS1 to PEM:

PemObjectpemObject=newPemObject("RSA PRIVATE KEY",privateKeyPKCS1);StringWriterstringWriter=newStringWriter();PemWriterpemWriter=newPemWriter(stringWriter);pemWriter.writeObject(pemObject);pemWriter.close();StringpemString=stringWriter.toString();

Check with command line OpenSSL that the key format is as expected:

openssl rsa-in rsa_private_key.pem-noout-text

Public key

Convert public key from X.509 SubjectPublicKeyInfo to PKCS1:

PublicKeypub=pair.getPublic();byte[]pubBytes=pub.getEncoded();SubjectPublicKeyInfospkInfo=SubjectPublicKeyInfo.getInstance(pubBytes);ASN1Primitive primitive=spkInfo.parsePublicKey();byte[]publicKeyPKCS1=primitive.getEncoded();

Convert public key in PKCS1 to PEM:

PemObjectpemObject=newPemObject("RSA PUBLIC KEY",publicKeyPKCS1);StringWriterstringWriter=newStringWriter();PemWriterpemWriter=newPemWriter(stringWriter);pemWriter.writeObject(pemObject);pemWriter.close();StringpemString=stringWriter.toString();

Check with command line OpenSSL that the key format is as expected:

openssl rsa-in rsa_public_key.pem-RSAPublicKey_in-noout-text

Thanks

Many thanks to the authors of the following posts:

https://stackoverflow.com/a/8713518/1016580

https://stackoverflow.com/a/14052651/1016580

https://stackoverflow.com/a/14068057/1016580

Those posts contained useful, though sometimes outdated info (i.e. for older versions of BouncyCastle), that helped me to construct this post.