* @return a Map with Subject, public-key and challenge
*/
public static Map processSPKAC(String spkac) throws IOException, NoSuchAlgorithmException, InvalidKeyException, SignatureException, Exception {
Map map = new HashMap();
byte[]data = Base64.decode(spkac);
ASN1InputStream ais = new ASN1InputStream(new ByteArrayInputStream(data));
DERSequence spkacSeq = (DERSequence)ais.readObject();
// SPKAC = SEQ {PKAC, SIGN-ALG, SIGN}
// Get PKAC and obtain PK and C
DERSequence pkacSeq = (DERSequence)spkacSeq.getObjectAt(0);
DERObject pk = (DERObject)pkacSeq.getObjectAt(0);