EMVVerifyPin.java

/**
     * The VERIFY command is used for OFFLINE authentication.
     * The Transaction PIN Data (input) is compared with the Reference PIN Data
     * stored in the application (ICC).
     *
     * NOTE: The EMV command "Offline PIN" (plaintext) is vulnerable to a Man-in-the-middle attack.
     * Terminals should request online pin verification instead (or encipher PIN) !!
     *
     * Case 3 C-APDU
     *
     * @param pin the PIN to verify
     * @param transmitInPlaintext
     * @return
     */
    public static byte[] verifyPIN(char[] pin, boolean transmitInPlaintext) {
        if (pin.length < 4 || pin.length > 12) { //0x0C
            throw new RuntimeException("Invalid PIN length. Must be in the range 4 to 12. Length=" + pin.length);
        }
        for(char c : pin){
            if(!Character.isDigit(c)) {
                throw new RuntimeException("Only decimal digits allowed in PIN");
            }
        }
        byte[] cmd = new byte[13];
        cmd[0] = 0x00;
        cmd[1] = 0x20;
        cmd[2] = 0x00;

        //EMV book 3 Table 23 (page 88) lists 7 qualifiers,
        //but only 2 are relevant in our case (hence the use of boolean)
        byte p2QualifierPlaintextPIN = (byte) 0x80;
        byte p2QualifierEncipheredPIN = (byte) 0x88;
        if (transmitInPlaintext) {
            cmd[3] = p2QualifierPlaintextPIN;
            cmd[4] = 0x08; //Lc
            cmd[5] = (byte)(0x20 | pin.length); //Control field (binary 0010xxxx)
            //The remaining 8 bytes is the plaintext Offline PIN Block. This block is split into nibbles (4 bits)
            Arrays.fill(cmd, 6, cmd.length, (byte)0xFF); //Filler bytes

            boolean highNibble = true; //Alternate between high and low nibble
            for (int i = 0; i < pin.length; i++) { //Put each PIN digit into its own nibble
                int pos = i / 2;
                int digit = Character.digit(pin[i], 10);
                if (highNibble) {
                    cmd[6 + pos] &= (byte) 0x0F; //Clear bits
                    cmd[6 + pos] |= (byte) (digit << 4);

                } else {
                    cmd[6 + pos] &= (byte) 0xF0; //Clear bits
                    cmd[6 + pos] |= (byte) (digit);
                }
                highNibble = !highNibble;
            }

        } else {
            cmd[3] = p2QualifierEncipheredPIN;
            //Encipher PIN
            //TODO: Implement enciphered PIN
            throw new UnsupportedOperationException("Enciphered PIN not implemented");
        }

        return cmd;
    }