Hi Jakub, On 3/17/23 22:31, Jakub Wilk wrote: > * Alejandro Colomar <alx.manpages@xxxxxxxxx>, 2023-01-01 17:27: >> arc4random_uniform() returns a random number less than upper_bound for >> valid input, or 0 when upper_bound is invalid. > > Is the "or 0 ..." thing part of the API? Yes, it is part of the (undocumented) API. At least, their authors claim to have thought about it when designing it, and purposefully took the decision of returning 0. They fail to acknowledge that it's a bug, also fail to acknowledge that their documentation doesn't document this behavior, and don't have any intention of changing the API because "we don't know what can possibly fail; you'd have to audit all software in the world to confirm that none depends on that detail". I have serious doubts that any software can depend on that, because mathematically it doesn't make any sense, so algorithms will likely have to purposefully special-case arc4random_uniform(0), but can't know for sure, because well, I haven't audited all software in the world. I didn't find any case in OpenBSD's source code that depends on that, however. > I could find anything like that > in glibc docs or BSD man pages. <https://inbox.sourceware.org/libc-alpha/20230101162627.28031-1-alx@xxxxxxxxxx/> Their manual page is bogus, and the funny thing is that one of Theo's arguments to reject a proposal to fix the bug in the API was that I wouldn't be able to document it reasonably. Well, as you saw, it's the current behavior that isn't well documented, and I had to special-case it in BUGS. > >> STANDARDS >> These nonstandard functions are present in several Unix systems. > > That's not really helpful. Also, the VERSIONS section is missing ("every > new interface should include a VERSIONS section"). I thought of that this morning, while doing some reorganization of that section globally. I'll add the version. > > In contrast, the libbsd man page is much more informative: > >> These functions first appeared in OpenBSD 2.1, FreeBSD 3.0, NetBSD >> 1.6, and DragonFly 1.0. The functions arc4random(), arc4random_buf() >> and arc4random_uniform() appeared in glibc 2.36. Yup. :) Thanks a lot for this thorough review! Alex >> >> The original version of this random number generator used the RC4 (also >> known as ARC4) algorithm. In OpenBSD 5.5 it was replaced with the >> ChaCha20 cipher, and it may be replaced again in the future as >> cryptographic techniques advance. A good mnemonic is “A Replacement >> Call for Random”. > -- <http://www.alejandro-colomar.es/> GPG key fingerprint: A9348594CE31283A826FBDD8D57633D441E25BB5
Attachment:
OpenPGP_signature
Description: OpenPGP digital signature
