For digital signatures private key cryptosystem is used.

Pretty Good Privacy (PGP) uses a combination of public-key and symmetric-key cryptography to encrypt and decrypt data.  Public key cryptography uses two keys: a public key for encryption and a private key for decryption. The public key is known publicly, while only the user knows the private key. When a user sends a message using their public key, it is encrypted. The recipient can decrypt the message using their private key.  PGP is based on a combination of public key or asymmetric cryptography and symmetric cryptography. Asymmetric cryptography uses a pair of related keys, with the... Show more

Pretty Good Privacy (PGP) uses a combination of public-key and symmetric-key cryptography to encrypt and decrypt data. 

Public key cryptography uses two keys: a public key for encryption and a private key for decryption. The public key is known publicly, while only the user knows the private key. When a user sends a message using their public key, it is encrypted. The recipient can decrypt the message using their private key. 
PGP is based on a combination of public key or asymmetric cryptography and symmetric cryptography. Asymmetric cryptography uses a pair of related keys, with the private key kept secret. The private key can be used to decrypt messages and generate digital signatures. 

Phil Zimmermann created the first version of PGP encryption in 1991. The name comes from a grocery store named "Ralph's Pretty Good Grocery" in Garrison Keillor's fictional town, Lake Wobegon. 

Here are some things to know about PGP:
PGP encryption is secure.
PGP uses a variation of the public key system.
PGP uses strong encryption methods, so it doesn't retrieve forgotten passwords, which can result in lost messages or files.
PGP can be difficult to use because it takes time and effort to fully encrypt data and files.
If an organization is considering deploying PGP, it has to train its employees.

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