Cryptographic Key Length Recommendation

In most cryptographic functions, the key length is an important security parameter. Both academic and private organizations provide recommendations and mathematical formulas to approximate the minimum key size requirement for security. Despite the availability of these publications, choosing an appropriate key size to protect your system from attacks remains a headache as you need to read and understand all these papers.

This web site implements mathematical formulas and summarizes reports from well-known organizations allowing you to quickly evaluate the minimum security requirements for your system. You can also easily compare all these techniques and find the appropriate key length for your desired level of protection. The lengths provided here are designed to resist mathematic attacks; they do not take algorithmic attacks, hardware flaws, etc. into account.

Choose a Method
1   Reference for the comparison
You can enter the year until when your system should be protected and see the corresponding key sizes or you can enter a key/hash/group size and see until when you would be protected.
2
Method Date Symmetric Factoring
Modulus
Discrete Logarithm
Key Group
Elliptic Curve Hash
[1] Lenstra / Verheul (?) 2016 83
1664 1312
146 1664
155 165
[2] Lenstra Updated (?) 2016 79
1273 1392
158 1273
158 158
[3] ECRYPT II 2016 - 2020 96 1776
192 1776
192 192
[4] NIST 2011 - 2030 112 2048
224 2048
224 224
[5] ANSSI 2014 - 2020 100 2048
200 2048
200 200
[6] NSA - - -
- -
- -
[7] RFC3766 (?) - - -
- -
- -
[8] BSI 2016 128 2048
256 2048
256 256
All key sizes are provided in bits. These are the minimal sizes for security.
© 2016 BlueKrypt - v 29.2 - September 17, 2015
Author: Damien Giry
Approved by Prof. Jean-Jacques Quisquater
Contact:
I would like to thank Prof. Arjen K. Lenstra for his kind authorization and comments.
Surveys of laws and regulations on cryptology: Crypto Law Survey / Digital Signature Law Survey.
Bibliography[1] Selecting Cryptographic Key Sizes, Arjen K. Lenstra and Eric R. Verheul, Journal Of Cryptology, vol. 14, p. 255-293, 2001.
[2] Key Lengths, Arjen K. Lenstra, The Handbook of Information Security, 06/2004.
[3] Yearly Report on Algorithms and Keysizes (2012), D.SPA.20 Rev. 1.0, ICT-2007-216676 ECRYPT II, 09/2012.
[4] Recommendation for Key Management, Special Publication 800-57 Part 1 Rev. 3, NIST, 07/2012.
[5] Mécanismes cryptographiques - Règles et recommandations, Rev. 2.03, ANSSI , 02/2014.
[6] Fact Sheet Suite B Cryptography, NSA, 08/2015.
[7] Determining Strengths for Public Keys Used for Exchanging Symmetric Keys, RFC 3766, H. Orman and P. Hoffman, 04/2004.
[8] Kryptographische Verfahren: Empfehlungen und Schlüssellängen, TR-02102-1 v2015-1, BSI, 02/2015.
Privacy Policy (P3P)  |  Disclaimer / Copyright  |  Release Notes