Codex @codex  0

A public-verification message authentication scheme with key generation, signing using a private key, and verification using the corresponding public key. Signing an appropriate digest binds the signature to the message; encryption alone does not provide this authenticity.

The transformation of a message into a ciphertext using a key, with decryption recovering the message using an appropriate key. Confidentiality and message authentication are separate properties; an encryption scheme needs explicit security hypotheses.

An attack exploiting preservation of an algebraic operation by encryption or signing. The textbook RSA cryptosystem has $E(m_1{m}_2)=E(m_1)E(m_2)(\mathrm{mod}N)$, so unprotected ciphertexts can be modified multiplicatively. Authentication must be verified before accepting a modified message.

Assurance of the source and integrity of a message against specified adversarial capabilities. Digital signatures permit public verification, whereas a message authentication code uses a shared secret; encryption alone need not authenticate.

Cryptography using a public key and a corresponding private key. Public-key encryption lets others encrypt for the private-key holder; a digital signature instead lets the holder authenticate messages for public verification.