Update ZCrypto, thereby allowing parsing of RSA public keys with very large exponents

[phillip-stephens]

As reported in #670, we were unable to parse RSA keys with very large exponents (larger than Go's int). The fix was to bring in the crypto/rsa into zcrypto and update it to use big.Int.

How to Test

I created Dockerfile to create an SSH and TLS server with RSA encryption and large values for E. I confirmed that on master I get:

{"ip":"127.0.0.1","port":2222,"data":{"ssh":{"status":"handshake-error","protocol":"ssh","port":2222,"timestamp":"2026-05-14T16:56:43+12:00","error":"failed to create SSH client connection: ssh: handshake failed: ssh: exponent too large"}}}

TLS

...
"error":"could not successfully complete tls handshake for target 127.0.0.1: tls: failed to parse certificate from server: asn1: structure error: integer too large"}}}

And after fix parsing happens correctly:

"subject_key_info":{"key_algorithm":{"name":"RSA"},"rsa_public_key":{"exponent":18055167462020576832540418801269399449497458945579819352363471260881145217415187933979886593216702486709838548298363314547135313727007388848848718877325958711188766129904621880761442689187401184009426273984277684003122213085277946304575120619200203923589966657977707649865400135198719640242827758871490643836453581086290290070463208430162495075066127540155058688548796517517682461188204549669427084215413151090479072676858203077338724804689901318804911869834305119181949193084540411547590690852877796014237632488428719014037051865845914633544290925724386331615109209841,"modulus":"...","length":2048},"fingerprint_sha256":"6e5b1a90509c51ff8963a0ceb6771724c074b7445eb9523e3f524cbc8aa8b25d"}

Issue Tracking

Resolves #670

[hdm]

howdy! i pulled this into runZeroInc/excrypto#78 as well - noticed a few small issues (other places where E was being limited); should be clear in the diffs if you'd like to pull these back too

[phillip-stephens]

Awesome, I'll pull those in, thank you!