Nonces are Noticed: AEAD Revisited

We draw attention to a gap between theory and usage of nonce-based symmetric encryption, under which the way the former treats nonces can result in violation of privacy in the latter. We bridge the gap with a new treatment of nonce-based symmetric encryption that modifies the syntax (decryption no longer takes a nonce), upgrades the security goal (asking that not just messages, but also nonces, be hidden) and gives simple, efficient schemes conforming to the new definitions. We investigate both basic security (holding when nonces are not reused) and advanced security (misuse resistance, providing best-possible guarantees when nonces are reused)

An Efficient Authenticating Short Encrypted Messages Using IND-CPA Algorithms

In today's age of information and technology , many applications can exchange network of information and communication. In Banking , educational, economical area can also exchange the information over the internet. The exchange of information is too risky to work from internet. So many hackers are try to stolen information from the internet. So there is must require data security and integrity over the internet.There are many authentication Technics are in information technology fields. Like HMAC , UMAC, etc.but all this authentication schemes are time consuming and less secure .so we propose more secure and less time consuming authentication codes that are more useful than any other message authentication code in the our literature survey . DOI: 10.17762/ijritcc2321-8169.15073

GOTCHA Password Hackers!

We introduce GOTCHAs (Generating panOptic Turing Tests to Tell Computers and Humans Apart) as a way of preventing automated offline dictionary attacks against user selected passwords. A GOTCHA is a randomized puzzle generation protocol, which involves interaction between a computer and a human. Informally, a GOTCHA should satisfy two key properties: (1) The puzzles are easy for the human to solve. (2) The puzzles are hard for a computer to solve even if it has the random bits used by the computer to generate the final puzzle --- unlike a CAPTCHA. Our main theorem demonstrates that GOTCHAs can be used to mitigate the threat of offline dictionary attacks against passwords by ensuring that a password cracker must receive constant feedback from a human being while mounting an attack. Finally, we provide a candidate construction of GOTCHAs based on Inkblot images. Our construction relies on the usability assumption that users can recognize the phrases that they originally used to describe each Inkblot image --- a much weaker usability assumption than previous password systems based on Inkblots which required users to recall their phrase exactly. We conduct a user study to evaluate the usability of our GOTCHA construction. We also generate a GOTCHA challenge where we encourage artificial intelligence and security researchers to try to crack several passwords protected with our scheme.Comment: 2013 ACM Workshop on Artificial Intelligence and Security (AISec

Cryptanalysis of the MEM Mode of Operation

The MEM mode is a nonce-based enciphering mode of operation proposed by Chakraborty and Sarkar, which was claimed to be secure against symmetric nonce respecting adversaries. We show that this is not correct by using two very simple attcks. One attack need one decryption and one decryption queries, and the other only need one encryption query

AE5 Security Notions: Definitions Implicit in the CAESAR Call

A draft call for the CAESAR authenticated-encryption competition adopts an interface that is not aligned with existing definitions in the literature. It is the purpose of this brief note to formalize what we believe to be the intended definitions

Nonce-Based Cryptography: Retaining Security when Randomness Fails

We take nonce-based cryptography beyond symmetric encryption, developing it as a broad and practical way to mitigate damage caused by failures in randomness, whether inadvertent (bugs) or malicious (subversion). We focus on definitions and constructions for nonce-based public-key encryption and briefly treat nonce-based signatures. We introduce and construct hedged extractors as a general tool in this domain. Our nonce-based PKE scheme guarantees that if the adversary wants to violate IND-CCA security then it must do both of the following: (1) fully compromise the RNG (2) penetrate the sender system to exfiltrate a seed used by the sende

ZETA: Towards Tagless Authenticated Encryption

Tag-based message authentication is a popular cryptographic technique to digitally sign messages. However, for short messages, it often incurs additional costs due to large tags. In this paper, we propose a new scheme that achieves tagless message authentication. The scheme leverages a trade-off between character support and complexity of forgery to provide information security and authenticity

A Practical Forgery Attack on Lilliput-AE

Lilliput-AE is a tweakable block cipher submitted as a candidate to the NIST lightweight cryptography standardization process. It is based upon the lightweight block cipher Lilliput, whose cryptanalysis so far suggests that it has a large security margin. In this note we present an extremely efficient forgery attack on Lilliput-AE: Given a single arbitrary message of length about 2^36 bytes, we can instantly produce another valid message that leads to the same tag, along with the corresponding ciphertext. The attack uses a weakness in the tweakey schedule of Lilliput-AE which leads to the existence of a related tweak differential characteristic with probability 1 in the underlying block cipher. The weakness we exploit, which does not exist in Lilliput, demonstrates the potential security risk in using a very simple tweakey schedule in which the same part of the key/tweak is re-used in every round, even when round constants are employed to prevent slide attacks. Following this attack, the Lilliput-AE submission to NIST was tweaked