How to get PublicKey from PKCS10CertificationReque

Question

In the new version of Bouncy Castle library there are changes in PKCS10CertificationRequest. In previous versions it was possible to get PublicKey from such request using getPublicKey() method (see old doc).

Now this method disappered. How can I get PublicKey from with from such request? There is getSubjectPublicKeyInfo().parsePublicKey() but it returns ASN1Primitive.

I see that from SPKAC NetscapeCertRequest I still can read PublicKey directly by calling getPublicKey().

Answer 1

There is a utility class in the main provider package called PublicKeyFactory. The method createKey returns an AsymmetricKeyParameter which you cast to whatever type of public key is appropriate, e.g.

SubjectPublicKeyInfo pkInfo = pkcs10CertReq.getSubjectPublicKeyInfo();
RSAKeyParameters rsa = (RSAKeyParameters) PublicKeyFactory.createKey(pkInfo);

EDIT 1:

In addition, to create a java.security.PublicKey a few more steps are needed:

RSAPublicKeySpec rsaSpec = new RSAPublicKeySpec(rsa.getModulus(), rsa.getExponent());
KeyFactory kf = KeyFactory.getInstance("RSA");
PublicKey rsaPub = kf.generatePublic(rsaSpec);

Answer 2

PKCS10CertificationRequest csr =...;    
PublicKey pk = KeyFactory.getInstance("RSA").generatePublic(new X509EncodedKeySpec(csr.getSubjectPublicKeyInfo().toASN1Primitive().getEncoded()));

RFC 2986 - PKCS #10: Certification Request Syntax

CertificationRequestInfo ::= SEQUENCE {
version INTEGER { v1(0) } (v1,...),
subject Name,
subjectPKInfo SubjectPublicKeyInfo{{ PKInfoAlgorithms }},
attributes [0] Attributes{{ CRIAttributes }}
}

SubjectPublicKeyInfo { ALGORITHM : IOSet} ::= SEQUENCE {
algorithm AlgorithmIdentifier {{IOSet}},
subjectPublicKey BIT STRING
}

and then, you can see the document of java.security.spec.X509EncodedKeySpec

SubjectPublicKeyInfo ::= SEQUENCE {
algorithm AlgorithmIdentifier,
subjectPublicKey BIT STRING }

so you will know the encoding of this public key is X.509. and then change it to X509EncodedKeySpec and generate public key by keyFactory

Answer 3

What about using JcaPKCS10CertificationRequest?

JcaPKCS10CertificationRequest jcaPKCS10CertificationRequest = new JcaPKCS10CertificationRequest(pkcs10CertReq);
PublicKey publicKey = jcaPKCS10CertificationRequest.getPublicKey();

Answer 4

I was looking at the same issue, and this will work too (with the advantage that we don't need to specify the algorithm):

SubjectPublicKeyInfo pkInfo = pkcs10CertReq.getSubjectPublicKeyInfo();
JcaPEMKeyConverter converter = new JcaPEMKeyConverter();
PublicKey pubKey = converter.getPublicKey(pkInfo);

See org.bouncycastle.openssl.jcajce.JcaPEMKeyConverter