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
Compare all Methods
1   Reference for the comparison
2
Method Date Symmetric Asymmetric
Discrete Logarithm
Key Group
Elliptic Curve Hash
[1] Lenstra / Verheul (?) 2010 78
1369 1056
138 1369
146 155
[2] Lenstra Updated (?) 2010 75
1112 1152
150 1112
150 150
[3] ECRYPT II 2009 - 2012 80 1248
160 1248
160 160
[4] NIST 2007 - 2010 80 1024
160 1024
160 224
[5] FNISA 2009 - 2010 80 1536
160 1536
160 160
[6] NSA - - -
- -
- -
[7] RFC3766 (?) - - -
- -
- -
[8] BSI (signature only) 2010 - 1728
224 2048
224 160
All key sizes are provided in bits. These are the minimal sizes for security.
© 2010 BlueKrypt - v 24.6 - January 9, 2010
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, PKC2000: p. 446-465, 01/2000.
[2] Handbook of Information Security, Arjen K. Lenstra, 06/2004.
[3] Yearly Report on Algorithms and Keysizes (2009), D.SPA.7 Rev. 1.0, ICT-2007-216676 ECRYPT II, 07/2009.
[4] Recommendation for Key Management, Special Publication 800-57 Part 1, NIST, 03/2007.
[5] Mécanismes cryptographiques - Règles et recommandations "standards", Rev. 1.10, FNISA , 12/2006.
[6] Fact Sheet Suite B Cryptography, NSA, 09/2009.
[7] Determining Strengths for Public Keys Used for Exchanging Symmetric Keys, RFC 3766, H. Orman and P. Hoffman, 04/2004.
[8] Algorithms for Qualified Electronic Signatures, BNetzA, BSI, 01/2009 updated with this draft, BSI, 08/2009
Privacy Policy (P3P)  |  Disclaimer / Copyright  |  Release Notes