package pkcs12: Authentication bypass in Decode functions

Decode, DecodeChain, DecodeTrustStore, and ToPEM can incorrectly accept PKCS#12 files which were encoded with the wrong password, due to a failure to reject excessively-short PBMAC1 keys. Users who decode PKCS#12 files from untrusted sources and rely on the password for authentication can be tricked into accepting malicious PKCS#12 files. Users who only decode PKCS#12 files from trusted sources are not affected.

Thanks to Pavol Žáčik (Red Hat) and Alex Gaynor (Anthropic) for finding and reporting the same issue in OpenSSL (CVE-2026-34181).