You will need BouncyCastle:
import org.bouncycastle.asn1.ASN1Encodable;
import org.bouncycastle.asn1.ASN1Primitive;
import org.bouncycastle.asn1.pkcs.PrivateKeyInfo;
import org.bouncycastle.asn1.x509.SubjectPublicKeyInfo;
import org.bouncycastle.util.io.pem.PemObject;
import org.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:
PrivateKey priv = pair.getPrivate();
byte[] privBytes = priv.getEncoded();
PrivateKeyInfo pkInfo = PrivateKeyInfo.getInstance(privBytes);
ASN1Encodable encodable = pkInfo.parsePrivateKey();
ASN1Primitive primitive = encodable.toASN1Primitive();
byte[] privateKeyPKCS1 = primitive.getEncoded();
Convert private key in PKCS1 to PEM:
PemObject pemObject = new PemObject("RSA PRIVATE KEY", privateKeyPKCS1);
StringWriter stringWriter = new StringWriter();
PemWriter pemWriter = new PemWriter(stringWriter);
pemWriter.writeObject(pemObject);
pemWriter.close();
String pemString = 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:
PublicKey pub = pair.getPublic();
byte[] pubBytes = pub.getEncoded();
SubjectPublicKeyInfo spkInfo = SubjectPublicKeyInfo.getInstance(pubBytes);
ASN1Primitive primitive = spkInfo.parsePublicKey();
byte[] publicKeyPKCS1 = primitive.getEncoded();
Convert public key in PKCS1 to PEM:
PemObject pemObject = new PemObject("RSA PUBLIC KEY", publicKeyPKCS1);
StringWriter stringWriter = new StringWriter();
PemWriter pemWriter = new PemWriter(stringWriter);
pemWriter.writeObject(pemObject);
pemWriter.close();
String pemString = 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:
- http://stackoverflow.com/a/8713518/1016580
- http://stackoverflow.com/a/14052651/1016580
- http://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Those posts contained useful, though sometimes outdated info (i.e. for older versions of BouncyCastle), that helped me to construct this post.