SMIME Decryption

Question

I'm currently using a certificate for USER A to encrypt emails sent to USER B and USER B is still able to decrypt them.

How is this possible? USER A and USER B have different certificates issued from the same CA.

Thanks in advance.

Answer 1

Email encryption is mostly done using public-key encryption. That means that the sender has a certificate with the receivers public-key which is used to encrypt the message being sent. The receiver will receive the encrypted message and use her/his private-key to decrypt the message. The message encrypted in this fashion will only be visible to the receiver but not other receivers who do not posses the private key. The configurations for encryption /decryption is normally saved in email clients like Thunderbird (under settings!)

http://en.wikipedia.org/wiki/Email_encryption

The certificate you are using must be a public-key belonging to the reciever or else a generic key that can be decrypted by any certificate or no real encryption key at all.