Add runtime validation for cryptographic fields across the codebase

[coderabbitai]

As discussed in PR #765, we should consider adding runtime validation to ensure cryptographic fields such as public keys and signatures meet specific format requirements throughout the codebase.

This enhancement would improve security and prevent potential issues due to incorrect formats.

Reference comment: #765 (comment)

cc @mvadari

[mvadari]

Closed in favor of #766.