1. Signature error: Signature error refers to the inconsistency between the digital signature of the transmitted information and the signature of the receiver's digital certificate, which is usually caused by the loss, invalidation or inconsistency of the receiver's digital certificate.
2. Data tampering: If the transmitted data is tampered with on the way, the digital signature is illegal, so the verification will fail.
3. Data transmission error: Digital signature is based on a certain data transmission protocol and encryption algorithm. If there is an error in data transmission, signature verification may fail.