[Sls-sea-dls] Exclusive CMAC use in SDLS

[Antonios Atlasis]

Dear Brian,

I am afraid I cannot enlighten you about the historical discussions (these may have taken place before myself joining the group), but my understanding, also by reading the corresponding blue books, is that while indeed CMAC is prescribed as baseline mode with TC (Page E-2) , HMAC is also included in CCSDS Blue book (page 6-2); so this is aligned with HMAC with SHA2 inclusion  in crypto Blue book (section 4.2.2).

Regarding potential reasons for baselining CMAC for authentication, (here I am speculating)  on top  of what you mentioned (sharing same primitive with other AES based implementations, which can facilitate industry implementation), it could also be that CMAC in some implementations provides very high throughput (if this is needed, of course)

Regards

Antonis

__________________________________________
Dr Antonios Atlasis
Hd. System Security Section (TEC-SES)
End-to-End Systems Division
Directorate of Technology, Engineering and Quality

European Space Research and Technology Centre (ESTEC)
Keplerlaan 1, PO Box 299
NL-2201 AZ Noordwijk, The Netherlands
T  +31 71 565 6095
M +31 61 873 5554

From: SLS-SEA-DLS <sls-sea-dls-bounces at mailman.ccsds.org> On Behalf Of Sipos, Brian J. via SLS-SEA-DLS
Sent: 03 November 2025 18:09
To: sls-sea-dls at mailman.ccsds.org
Subject: [Sls-sea-dls] Exclusive CMAC use in SDLS

SDLS WG,
I'm posting a question to the mailing list because I'm not able to search the mail archive and haven't come across any discussion on this topic in recent years looking through the archives manually.

The current SDLS blue books and green book prescribe a single variation of AES-GCM for AEAD and AES-CMAC for authentication. Was there any earlier discussion about other authentication methods (e.g. HMAC with SHA2...) that led to the current books? Or was it deemed more consistent to use CMAC because of the shared AES primitive with the AEAD cipher suite?

I'm asking from the perspective of the full list of approved algorithms from FIPS 140-3 [1] under Section 6.2.6, which includes some block cipher based (including CMAC) and some hash based, and which primitives in that list would be more or less acceptable to CCSDS community because of technical limitations, required conformances, historical reasons, etc.

Thanks for any feedback or pointers to earlier mailing list discussion about this.
Brian S.

[1] https://csrc.nist.gov/Projects/cryptographic-module-validation-program/sp-800-140-series-supplemental-information/sp800-140c

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