Read algorithm preferences
05Want-Content-Digest and Want-Repr-Digest express interest and weighted algorithm preferences. They can appear in requests or responses.
A server response can contain Want-Repr-Digest. The arrow points toward the client; a later client request may then carry Repr-Digest.
Source for this drawing: RFC 9530 · Read RFC section 4 ↗
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A message needs an address.
Think of a packet as a small addressed envelope. Devices pass it onward; transport protocols decide what delivery promises an application gets.
Helpful first, if these ideas are unfamiliar
These pictures are analogies to help you learn. The linked RFC explains the actual rules.
Terms in this drawing
Related RFCs and changes
“Updates” changes part of an earlier RFC. “Obsoletes” replaces it. This list shows selected related documents.
Preference values are Integers from 0 through 10: 1 is least preferred, 10 most preferred, and 0 means not acceptable.
- Preference values are Integers from 0 through 10: 1 is least preferred, 10 most preferred, and 0 means not acceptable.
- Preferences are only hints. The recipient can ignore them, use another algorithm or omit the Integrity field; ignored preferences are not a protocol error.
- A preference in a server response asks the client for the respective Integrity field in future requests. Applications can impose additional requirements, but this RFC mandates no particular rejection status.
Examples use SHA-256 and SHA-512 from the RFC’s initial Active registry entries. md5 is shown only as a not-acceptable preference; it is Deprecated in that registry. Old Want-Digest and Digest are obsoleted, not alternative spellings of these new fields.
Read the RFC section ↗