Native Encription

[dushantha12]

Hi,

I am developing smart card based system using C. In my case I have to do 3 pass authentication. My problem is with challenge generation process. I can get the random B and decrypt it and generate random A. Now I want to generate challenge. But I don't know how to make the challenge.

I have,

Random B
Random A

0x0000000000000000 as Initial Vector (8 bytes).

0x12121212121212123434343434343434 as Des Key (16 bytes).

Please tell me what is the process of generating challenge block (for DES).

Thank you.

[kbw]

That's not really enough information to answer your problem. If you don't really know much about cryptography, you're going to make the same mistakes as those in the past.

DES has a 56bit (7byte) key. So it makes no sense providing a 16byte key. Plus DES isn't secure anyway. It's normal to use Triple-DES (sometimes called 3DES). In which case a 16 bit might be used, the first 8 bytes is used in stages 1 and 3, and the second in stage 2.

At any rate, you need to get familiar with the subject before designing a security system, otherwise whatever you come up with won't be secure.

[ajh32]

If I were you I would investigate the OpenSSL library:

http://www.openssl.org/

[dushantha12]

Hi,

Thanks for your help. Yes it is my mistake. It's not DES it's TDEA. Now I can do host authentication using MIFARE SAM AV1.

This is the steps.

IV = 0x0000000000000000
Key = 0x12121212121212125656565656565656

random A = 0x0A1A2A3A4A5A6A7A
shifted random B = 0x1B2B3B4B5B6B7B0B

step 1:

XOR_block_one = random A XOR IV

step 2:

ENCRIPTED_block_one = encryption ( XOR_block_one , Key )

step 3:

XOR_block_two = shifted random B XOR ENCRIPTED_block_one

step 4:

ENCRIPTED_block_two = encryption ( XOR_block_two , Key )

step 5:

challenge = ENCRIPTED_block_one + ENCRIPTED_block_two

NOTE : In my case it is Host SAM authentication and I have 16byte length randA+randB(Shift) to encrypt.

Thank you.