Analysis of modern Cryptographic Hash Functions

Cryptographic hash functions are a security-critical building block for e-commerce and e-government systems. For example, when a document is signed by means of a digital signature (electronic signature), firstly hash functions are used to compress the document to a `fingerprint.` For performance reasons, the real signature is made on the fingerprint of the document only. For security reasons, it is of utmost importance that no two documents can be created which result in the same fingerprint. When this happens, this called a collision. While the existence of collisions can`t be avoided, due to the nature of the compression functions used, the design goal of a cryptographic hash function is to make it infeasible to construct such collisions. Currently, almost all applications use as hash function either RIPEMD-160, SHA-1, or MD5. It is known that MD5 should be used only in situations where backwards compatibility is required. SHA-1 is a standard proposed by the US federal administration. Recent breakthroughs in cryptanalysis have shown that many cryptographic hash functions are not as secure as previously believed. Collisions have been constructed for several designs, but not for SHA-1, yet. In this project, we will investigate the security of SHA-1 and several recently proposed alternatives. Our evaluation methods will be based on the recent developments in cryptanalysis. Secondly, we will extend the recently developed methods by establishing links to related fundamental problems in established mathematical fields like coding theory and solving of nonlinear equations over finite fields. By linking the security of hash functions to more fundamental problems, we will be able to obtain better bounds on their security level. Armed with these new insights, we will design and propose new alternatives to SHA-1, which will have an increased security level.

Cryptographic hash functions are a security-critical building block for e-commerce and e-government systems. For example, when a document is signed by means of a digital signature (electronic signature), firstly hash functions are used to compress the document to a `fingerprint.` For performance reasons, the real signature is made on the fingerprint of the document only. For security reasons, it is of utmost importance that no two documents can be created which result in the same fingerprint. When this happens, this called a collision. While the existence of collisions can`t be avoided, due to the nature of the compression functions used, the design goal of a cryptographic hash function is to make it infeasible to construct such collisions. Currently, almost all applications use as hash function either RIPEMD-160, SHA-1, or MD5. It is known that MD5 should be used only in situations where backwards compatibility is required. SHA-1 is a standard proposed by the US federal administration. Recent breakthroughs in cryptanalysis have shown that many cryptographic hash functions are not as secure as previously believed. Collisions have been constructed for several designs, but not for SHA-1, yet. In this project, we will investigate the security of SHA-1 and several recently proposed alternatives. Our evaluation methods will be based on the recent developments in cryptanalysis. Secondly, we will extend the recently developed methods by establishing links to related fundamental problems in established mathematical fields like coding theory and solving of nonlinear equations over finite fields. By linking the security of hash functions to more fundamental problems, we will be able to obtain better bounds on their security level. Armed with these new insights, we will design and propose new alternatives to SHA-1, which will have an increased security level.