Encryption is a method of changing plaintext (text that is readable by humans) into ciphertext (text that is meaningless to humans). There are many DIFFERENT ways of encryption, some stronger than others. Two main categories of encryption are SYMMETRIC and asymmetric. 

In symmetric CRYPTOGRAPHY, the same key that encrypts a file also decrypts it. In asymmetric cryptography, which is what PGP uses, one key (the public key) encrypts the file, and the other key (the private key) decrypts it. So, if user A wants to send an encrypted message to user B, user A would first obtain user B’s public key.

This is possible because public keys are meant to be widely distributed. Then user A encrypts the message using user B’s public key. The encrypted message can now only be decrypted with B’s private key, which only he possesses. Not even user A, who wrote the message, can decrypt what he has encrypted, because he does not possess user B’s private key. 

This ensures that the message is UNREADABLE by anyone other than user A. Encryption and signing are often combined. 

In this scenario, user A would use user B’s public key to encrypt the message, then use his own private key to sign the message. This will ensure that no one but user B can read the message, and when user B RECEIVES it, he can be assured that the message was not altered. To read the message, userB would first use user A’s public key to verify that the signature matches. 

Then user B would use his private key to decrypt the message that user A wrote.

Encryption is a method of changing plaintext (text that is readable by humans) into ciphertext (text that is meaningless to humans). There are many different ways of encryption, some stronger than others. Two main categories of encryption are symmetric and asymmetric. 

In symmetric cryptography, the same key that encrypts a file also decrypts it. In asymmetric cryptography, which is what PGP uses, one key (the public key) encrypts the file, and the other key (the private key) decrypts it. So, if user A wants to send an encrypted message to user B, user A would first obtain user B’s public key.

This is possible because public keys are meant to be widely distributed. Then user A encrypts the message using user B’s public key. The encrypted message can now only be decrypted with B’s private key, which only he possesses. Not even user A, who wrote the message, can decrypt what he has encrypted, because he does not possess user B’s private key. 

This ensures that the message is unreadable by anyone other than user A. Encryption and signing are often combined. 

In this scenario, user A would use user B’s public key to encrypt the message, then use his own private key to sign the message. This will ensure that no one but user B can read the message, and when user B receives it, he can be assured that the message was not altered. To read the message, userB would first use user A’s public key to verify that the signature matches. 

Then user B would use his private key to decrypt the message that user A wrote.