There is no encryption that is 100% immune. All encryption can have its key guessed, if the key is expressible in bits. This ensures that classical encryption schemes, even post-quantum ones, have a guessability or hardness in terms of the number of bits that must be correctly guessed at once in order to forge credentials.
This reasoning leads to export-grade cryptography, a bane of our praactice that nonetheless was an acceptable compromise for many years. It seems that that era of compromise is coming to an end, though.
"Export-grade encryption" was always a bad idea. You can block the export of stronger encryption schemes but nothing prevents them from being developed outside the country. The result is that all new and innovative crypto work gets done elsewhere, leaving your own country playing catch-up.
This reasoning leads to export-grade cryptography, a bane of our praactice that nonetheless was an acceptable compromise for many years. It seems that that era of compromise is coming to an end, though.