Problem transmiting a RSA public key, javaME , bouncy castle

Question

I\'m working on the porting of an instance messaging application from Java to JavaME ,that also implements cryptography. The problem is that I want to send my public key to

Answer 1

DER-encoding is just a standard for encoding. Saying that a key is DER-encoded is equivalent to saying it is XML-encoded: you need to agree on how it is DER-/XML-encoded to be able to decode it.

In this case your RSAPublicKeyStructure.getEncoded() returns the key as the DER-encoding of an ASN.1 RSAPublicKey:

RSAPublicKey ::= SEQUENCE {
  modulus INTEGER, -- n
  publicExponent INTEGER -- e 
}

The X509EncodedKeySpec on the other hand expects to be handed the DER-encoding of an ASN.1 PublicKeyInfo:

PublicKeyInfo ::= SEQUENCE {
  algorithm AlgorithmIdentifier,
  PublicKey BIT STRING
}

To create a PublicKeyInfo using BouncyCastle do this (courtesy of GregS):

RSAPublicKeyStructure rsaPublicKey = /* ... */
AlgorithmIdentifier rsaEncryption = new AlgorithmIdentifier(PKCSObjectIdentifiers.rsaEncryption, DERNull.INSTANCE); 
SubjectPublicKeyInfo publicKeyInfo = new SubjectPublicKeyInfo(rsaEncryption, rsaPublicKey);
byte[] encodedPublicKeyInfo = publicKeyInfo.getEncoded();