You might forget your GPG private key’s passphrase. You need your private key’s passphrase in order to decrypt an encrypted message or document which is encrypted using your public key. So, if you lost or forgot it then you will not be able to decrypt the messages or documents sent to you.
You don’t have to worry though. You can easily change/edit/update your GPG Passphrase. This can be done using –edit-key command.

If you lost your private key then your public key becomes useless because you will not be able to decrypt any encrypted message sent to you. You need to revoke your public key and let other users know that this key is no longer useful.
If you have uploaded your public key into HKP key-servers then you also need to notify the key-server about your key revocation.

Your public keyring becomes a long list after you go on importing other peoples’ keys into your system. Later on you might feel to delete some of them which are unnecessary.
You can do so (delete keys from your public keyring) with the following command:

Checksum is used to verify the data integrity of files. It can be used to detect errors while transmitting data between devices or over the internet. The checksum functions as a digital fingerprint of a file. Computer programs like md5sum and sha256sum calculate and verify checksum. md5sum calculates and verifies 128-bit MD5 hashes and sha1sum calculates and verifies SHA-1 hashes.
Verifying locally stored files

GNU Privacy Guard (GnuPG or GPG) is a free cryptographic software that can secure data transfer and communication between two parties by encrypting, signing and verifying data.

History
Public-key encryption makes key-management much easier. It was invented in 1976 by two Stanford mathematicians, Whitfield Diffie and Martin Hellman. Their discovery can be phrased simply: enciphering schemes should be asymmetric. For thousands of years all ciphers were symmetric—the key for encrypting a message was identical to the key for decrypting it, but used, so to speak, in reverse. To change “5 100 100 5 15 55” or “6 120 120 6 18 66” back into “attack,” for instance, one simply reverses the encryption by dividing the numbers with the …