Strong secrecy is a term used in

formal proof In logic and mathematics, a formal proof or derivation is a finite sequence of sentences (called well-formed formulas in the case of a formal language), each of which is an axiom, an assumption, or follows from the preceding sentences in the sequ ...

-based

cryptography Cryptography, or cryptology (from grc, , translit=kryptós "hidden, secret"; and ''graphein'', "to write", or ''-logia'', "study", respectively), is the practice and study of techniques for secure communication in the presence of adve ...

for making propositions about the security of

cryptographic protocol A security protocol (cryptographic protocol or encryption protocol) is an abstract or concrete protocol that performs a security-related function and applies cryptographic methods, often as sequences of cryptographic primitives. A protocol descr ...

s. It is a stronger notion of security than syntactic (or weak) secrecy. Strong secrecy is related with the concept of

semantic security In cryptography, a semantically secure cryptosystem is one where only negligible information about the plaintext can be feasibly extracted from the ciphertext. Specifically, any probabilistic, polynomial-time algorithm (PPTA) that is given the cip ...

or indistinguishability used in the computational proof-based approach. Bruno Blanchet provides the following definition for strong secrecy: :''Strong secrecy means that an adversary cannot see any difference when the value of the secret changes''Blanchet, B. (2004) Automatic proof of strong secrecy for security protocols. In proceedings of the IEEE Symposium on Security and Privacy, pp 86-100. https://www.di.ens.fr/~blanchet/publications/BlanchetOakland04.html For example, if a process encrypts a message ''m'' an attacker can differentiate between different messages, since their

ciphertexts In cryptography, encryption is the process of encoding information. This process converts the original representation of the information, known as plaintext, into an alternative form known as ciphertext. Ideally, only authorized parties can decip ...

will be different. Thus ''m'' is not a strong secret. If however,

probabilistic encryption Probabilistic encryption is the use of randomness in an encryption algorithm, so that when encrypting the same message several times it will, in general, yield different ciphertexts. The term "probabilistic encryption" is typically used in referen ...

were used, ''m'' would be a strong secret. The randomness incorporated into the encryption

algorithm In mathematics and computer science, an algorithm () is a finite sequence of rigorous instructions, typically used to solve a class of specific problems or to perform a computation. Algorithms are used as specifications for performing ...

will yield different ciphertexts for the same value of ''m''.

Notes

Cryptography {{crypto-stub

See also

Notes