In most cryptographic functions, key length is a substantial security parameter. Quite a few academic and official publications give recommendations and mathematical techniques to determine the minimum size of cryptographic keys while optimizing their security.

Although those publications are easily available, the choice of an appropriate key size remains complex as it depends on the reading and good understanding of the documents. allows you to determine the appropriate key length for a minimum security level through the implementation of the mathematical formulas with a summary of the information available in those publications. You can also easily compare the various methods.

  • Equations by Lenstra and Verheul: In 1999, professors Arjen K. Lenstra and Eric R. Verheul described mathematical formulas to assess the minimum size for the security of cryptographic keys. It is the first publication presenting a mathematical approach based on concrete parameters.
  • More recent equations by Lenstra: In 2004, Professor Arjen K. Lenstra described mathematical formulas allowing the minimum size for the security of cryptographic keys to be assessed. It updates the first edition. This method is easier to use as it reduces the number of parameters to be modified by the user.
  • ECRYPT II Recommendations: ECRYPT is a European network of excellence. Every year, ECRYPT II issues a report based on the security level targeted by the user. It uses among others the techniques used in the framework of the European project NESSIE.
  • NIST Recommendations: NIST is an agency of the US Trade Department. The results of this agency can be used by federal agencies. The report gathers crypto periods on 19 key types and recommendations on key sizes.
  • ANSSI Recommendations: This report gathers ANSSI (French National Agency for the security of information systems) recommendations concerning the security of information systems. It defines the position of the French government in terms of cryptographic quality.
  • "Suite B Cryptography" document from the NSA: The aim of the NSA is to define the basis of the cryptographic elements that allow creating products meeting the expectations of the American government. This is the Suite B, Suite A is not public.
  • Network Working Group RFC3766: Once the security level targeted is known, i.e. the size of the symmetric key to protect, this document explains how to calculate the minimal length of the corresponding asymmetric keys to achieve this security level.
  • BSI Recommendations: This report contains the recommendations of the German federal office for the security of information technologies.

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