DES Key Exchange

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1

Imported from previous forum

2

When using encryption method 2 with logon messages a master key is agreed upon by both parties in advance. How would one know the IVEC used for the same logon message? Would the parties need to set an IVEC in advance as well?

3

[ original email was from Ryan Pierce - rpierce@taltrade.com ]
> When using encryption method 2 with logon messages a master key is agreed upon by both parties in advance. How would one know the IVEC used for the same logon message? Would the parties need to set an IVEC in advance as well?

You are talking about using DES in ECB (Electronic Code Book) mode. ECB mode uses no initialization vector. The encryption function depends solely upon the 8-byte plaintext block, and the 56-bit key.

DES in CBC (Cipher Block Chaining) mode (i.e. PGP-DES-MD5) requires an Initialization Vector. Encryption in CBC mode depends upon the 8-byte plaintext block, the 56-bit key, and the previous 8 bytes of ciphertext (or, if the first encryption of the day, the Initialization Vector.)

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And to answer the first question, key exchange is done "out of band" (e.g. via letter in the mail, phone, etc).

> > When using encryption method 2 with logon messages a master key is agreed upon by both parties in advance. How would one know the IVEC used for the same logon message? Would the parties need to set an IVEC in advance as well?
>
> You are talking about using DES in ECB (Electronic Code Book) mode. ECB mode uses no initialization vector. The encryption function depends solely upon the 8-byte plaintext block, and the 56-bit key.
>
> DES in CBC (Cipher Block Chaining) mode (i.e. PGP-DES-MD5) requires an Initialization Vector. Encryption in CBC mode depends upon the 8-byte plaintext block, the 56-bit key, and the previous 8 bytes of ciphertext (or, if the first encryption of the day, the Initialization Vector.)
>