Mitigate MMA attacks on JWE RSA1_5 alg

[Vladimir Dzhuvinov]

See JOSE WG message

http://www.ietf.org/mail-archive/web/jose/current/msg01832.html

[Vladimir Dzhuvinov]

Added basic protection in commit 0e2cc15.

[Justin Richer]

From Juraj:

if (alg.equals(JWEAlgorithm.RSA1_5)) {
    int keyLength = cmkBitLength(readOnlyJWEHeader.getEncryptionMethod());
    SecretKey randomCMK = AES.generateAESCMK(keyLength);

    try {
        cmk = RSA1_5.decryptCMK(privateKey, encryptedKey.decode(), keyLength);
    } catch (Exception e) {
        // Protect against MMA attack by generating random CMK on failure,
        // see http://www.ietf.org/mail-archive/web/jose/current/msg01832.html
        cmk = randomCMK;
    }
}

[Vladimir Dzhuvinov]

Done in commit f74ec03 :)