Converting A public key in SubjectPublicKeyInfo format to RSAPublicKey format java

Question

The PublicKey.getEncoded(), returns a byte array containing the public key in SubjectPublicKeyInfo (x.509) format, how do i convert it to RSA public key encoding?

Solution 1

Use Bouncy Castle's SubjectPublicKeyInfo, like this:

byte[] encoded = publicKey.getEncoded();
SubjectPublicKeyInfo subjectPublicKeyInfo = SubjectPublicKeyInfo.getInstance(
        ASN1Sequence.getInstance(encoded));
byte[] otherEncoded = subjectPublicKeyInfo.parsePublicKey().getEncoded();

Solution 2

Without BouncyCastle:

PublicKey publicKey = KeyFactory.getInstance("RSA").generatePublic(new X509EncodedKeySpec(publicKeyBinary));                

Comments

[Ashish Kumar Shah]

This doesn't serve the pourpose. here we have just casted the public key into a RSAPublicKey object, but when i say RSAPublicKey.getEncoded(), i still get the key in x.509 format and not RSA format.

[Ashish Kumar Shah]

Thanks a bunch! Your approach worked. I am posting the exact snippet i used.

[ruckc]

The getPublicKey() is a deprecated function now.

[Manuel]

new SubjectPublicKeyInfo(..) is deprecated as well: Use SubjectPublicKeyInfo.getInstance(...). And instead of getPublicKey() use parsePublicKey().

[Maarten Bodewes]

The above comment from @AshishKumarShah seems incorrect; I do get a DER encoded key of course, but it does seem to be a PKCS#1 formatted key (ps Hi Martijn, hope everything is OK).

[martijno]

Hey Maarten. @AshishKumarShah's comment was probably about my answer before I edited (back in 2012 :) ).