Cryptography Stack Exchange is a question and answer site for software developers, mathematicians and others interested in cryptography. It's 100% free, no registration required.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

Is there a table (or a whitepaper from official sources) that compares the size of X509 certificates generated with RSA (starting from 1024 bits) and ECDSA (starting from 160 bits) ? Thanks for the support.

share|improve this question

migrated from Aug 23 '14 at 18:28

This question came from our site for information security professionals.

@MattNordhoff I have found on IETF, this slide Datagram Transport Layer Security in Constrained Environments. There are these certificate's sizes: ECDSA P-256: 91 bytes ECDSA P-384: 120 bytes ECDSA P-521: 156 bytes There aren't certificate's sizes of RSA 1024 (and lower and upper) and ECDSA P-160. How can i find these certificate sizes ? – Ellipticat Aug 23 '14 at 12:52
Ohhh. I totally misunderstood your question. I'm sorry. I think there have been one or two certificate size-related questions here or Crypto, but I don't have any information off the top of my head. I suppose you could create some certs and find out. It can be pretty variable depending on the meta data in the cert, no? (e.g. the length of your domain, of the CA's name...). – Matt Nordhoff Aug 23 '14 at 13:15
@MattNordhoff Maybe i have found what i wanted: An Introduction to the Uses of ECC-based Certificates on the Table 2 at page 5. What do you think ? Thanks for your answers. – Ellipticat Aug 23 '14 at 13:31
I do think that they should have mentioned that you would need point compression to reach those kind of differences. But personally I think that they just equated key strength with key size. I mean, I don't see any numbers for the domain parameters or public exponent either. Please take with a grain of salt. Note also that it makes quite a lot of difference if named curves are used or if the domain parameters are all present in the certificate; this makes comparison rather tricky. – Maarten Bodewes Aug 24 '14 at 0:26

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Browse other questions tagged or ask your own question.