PuTTY bug puttygen-zero-div

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summary: Occasional PuTTYgen division-by-zero errors
class: bug: This is clearly an actual problem we want fixed.
difficulty: taxing: Needs external things we don't have (standards, users etc)
priority: medium: This should be fixed one day.
present-in: 0.53 0.53b
fixed-in: 2003-06-29 61648131fb37777c927e955e4beb82665be1640f (0.54)

We are getting very occasional reports of integer division by zero errors in PuTTYgen.

15345.43775.42454.321823@chiark.greenend.org.uk
2001-11-13? (maybe already resolved)
3CA268CA.7258.2CA7836@localhost
SSH-1 1024, Win95, version 0.52 (assuming that, as we were told, `Teilungsfehler' is a division error)
000001c2bb51$77afcbf0$6401a8c0@lynn
SSH-2 RSA 2048, version ???

1645070571.20030227150247@inbox.ru
SSH-2 RSA 1024, version 0.53b
At last, we have a stack trace:

PUTTYGEN! 00408160()  sshbn.obj:_internal_mod
PUTTYGEN! 004086fa()  sshbn.obj:_bigdivmod
PUTTYGEN! 00408ecd()  sshbn.obj:_modinv
PUTTYGEN! 0041040f()  sshrsag.obj:_rsa_generate
PUTTYGEN! 004051c2()  puttygen.obj:_generate_rsa_key_thread@4
KERNEL32! 77e887dd()

SGT, 2003-06-28: Believed fixed. Thankfully, the bug was not in the bignum implementation (although I found a small bug in there too in the course of fixing it!) but in the much simpler prime-generation code that called it.

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Audit trail for this bug.

(last revision of this bug record was at 2016-12-27 11:40:22 +0000)