I want to calculate a cryptographic checksum using 3DES in outer CBC mode. As I know (and tried Googling also ) 3DES is an encryption algorithm, I'm not getting getting any information about how it can be used to calculate a checksum. Or may be I am missing some link here. Please correct me if I am wrong.
I need this to form over-the-air SMS.

  • So you want to do CBC-MAC or something differently?
    – SEJPM
    Commented Oct 17, 2015 at 11:40

1 Answer 1


3DES in outer CBC mode DES-EDE3-CBC (Page 6; here details in the application of ipsec/esp). Here's a code snippet for 3DES in outer CBC mode in a related application.

What you'll most likely have to do is to encrypt a message m using DES-EDE3-CBC and then throw away all but the last block of ciphertext (CBC-MAC). The iv is typically fixed at 0.

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