What two conditions must a digital signature meet?

Legibility and neatness are properties of handwritten signatures and have no relevance to digital signatures, which are mathematical values derived from cryptographic operations.

Digital signatures rely on asymmetric cryptography to guarantee two properties: authenticity (the signature proves the message came from the claimed sender, verified via the sender's public key) and unforgeability (only the holder of the private key can produce a valid signature, making it computationally infeasible to replicate without that key). These two properties are the foundational requirements defined in cryptographic standards for digital signatures.

Uniqueness alone is insufficient without authenticity, and 'special characters' is a concept from password policy, not digital signature requirements.

Digital signatures are fixed-length hash outputs determined by the algorithm (e.g., 256 bits for SHA-256), not by the length of any physical signature.