ABSTRACT
In private key encryption, there are two keys, one which is used to encrypt the plaintext data, and the other which is used to decrypt to ciphertext, getting back the original plaintext. Digital signing can be used to deal with one of the problems of public key encryption systems-guaranteeing that A's public key really does belong to A. The cost of getting a certificate is one major reason why small organizations tend not to use public-key encryption when they could. An app developer can provide both the app and its digital hash; someone who downloads it can recalculate the hash from the app code, and check that the answer matches the original hash to verify that the app hasn't been altered maliciously or corrupted in transit. There is regular discussion by government and law enforcement going like this: Encryption provides an opportunity for malefactors to conceal their communications with one another.
