CBOR tag 46010
The permanent reference for one entry in the IANA CBOR Tags registry. Not yet filed.
| Field | Value |
|---|---|
| Tag | 46010 |
| Data item | byte string, exactly 4 bytes |
| Semantics | CRC-32/ISO-HDLC digest |
| Reference | https://docs.1retro.com/iana/cbor-tag-46010/ |
| Range | First Come First Served |
| Contact | [email protected] |
Which CRC-32
Section titled “Which CRC-32”This tag is for one variant and no other: CRC-32/ISO-HDLC, the one zlib, PNG, gzip and every ROM DAT file compute.
| Parameter | Value |
|---|---|
| Polynomial | 0x04C11DB7, reflected |
| Initial value | 0xFFFFFFFF |
| Final XOR | 0xFFFFFFFF |
| Byte order | big-endian |
The four bytes read the same left to right as the hex string a DAT file writes. Another CRC-32 variant, Castagnoli’s among them, is a different algorithm and would take a tag of its own rather than share this one.
Why it is not in the COSE block
Section titled “Why it is not in the COSE block”IANA assigns bare-hash tags at 18300-18811, where the tag for COSE algorithm N is 18556 + N. COSE registers no
CRC-32 and no MD5, and the range of algorithm numbers that block maps is assigned by Standards Action, so neither will
ever appear there. This tag is taken instead from the First Come First Served range, where registration is a form and no
review.
CRC-32 is carried only to match a file against a catalog, never for integrity. Where these specifications need a digest to be trusted they name SHA-256 directly and offer no choice.