Existential forgery

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In a digital signature or Message Authentication Code (MAC) system, an existential forgery is the creation (by an adversary) of any message m and a valid signature (or MAC) σ for m, where m has not been signed or MACed in the past by the legitimate signer/MAC generator. The message m need not have any particular meaning, and indeed it may even be gibberish --- as long as the pair (m,σ) is valid, the adversary has succeeded in constructing an existential forgery.

Existential forgery is essentially the weakest adversarial goal, therefore the strongest schemes are those which are "existentially unforgeable."

[edit] See also

• Selective forgery
• Universal forgery