The digital signature can only be generated by the Bitcoin sender. It’s a series of tamper-proof code. By verifying this code, it proves that the transaction was initiated by the sender and not altered during the process.
Digital signature employs Digital Digest and Asymmetric Cryptography. Digital Digest compresses the information to a fixed length of code, then uses the private key to encrypt it, forming a digital signature.
After completion, it groups the transaction message with the signature and send it to the miners. Miners use the sender’s public key for verification. If it’s valid, it means he did initiate the transaction and it remains unaltered.
Asymmetric cryptography refers to using the private key for encryption and public key for decryption. It seems complicated but all you need to do is to enter the private key and voilà!