Re: Mandatory Algorithms for ESP?

["Derrell D. Piper" <[e-mail]>]

Charles,

Actually, the DOI is in error here.  The text under the DOI ESP section dates
from before SHA-1 was a mandatory authentication algorithm.  Since the AH
section (correctly) mandates MD5 and SHA-1, the correct interpretation for ESP
should be that support for both MD5 and SHA-1 are MUST's.

In summary, the following combinations are required by the IPSEC DOI:

   AH(HMAC-MD5)
   AH(HMAC-SHA)

   ESP_NULL(HMAC-MD5)
   ESP_NULL(HMAC-SHA)
   ESP_DES(<no integrity>)
   ESP_DES(HMAC-MD5)
   ESP_DES(HMAC-SHA)

>Also, do the terms "algorithm" and "transform" mean the same thing, or is there
>some subtle difference that I need to be aware of?

"Algorithm" is more general than "transform," in the sense that DES is the
base cryptographic algorithm used by the ESP_DES transform.  In other words,
the ESP_DES transform describes how to apply the DES algorithm in the ESP
context.  The resulting method, including things like how to do padding and IV
generation, results in a defined transform.

Derrell