3.2.2. Using ECC

Elliptic Curve Cryptography (ECC) is a cryptographic system that uses elliptic curves to create keys for encrypting data. ECC creates cryptographically-stronger keys with shorter key lengths than RSA, which makes it faster and more efficient to implement.
ECC has several advantages over RSA, since it is faster and requires shorter key lengths for stronger keys. The drawback to using ECC is that it is not as widely supported as RSA.

Table 3.1. Comparison of RSA and ECC Cipher Strength

Bits of Security[a] RSA Key Length ECC Key Length
80 1024 160-223
112 2048 224-255
128 3072 256-383
192 7860 384-511
256 15360 512+
[a] The information in this table is from the National Institute of Standards and Technology (NIST). For more information, see http://csrc.nist.gov/publications/nistpubs/800-57/SP800-57-Part1.pdf.

Certificate System supports using ECC with all of its subsystems, so ECC certificate requests can be submitted to CAs through any of the enrollment profiles and ECC keys can be archived and restored in the DRM. However, Certificate System does not include ECC support natively, so using ECC is slightly different than using RSA:
  • An external PKCS#11 module must be loaded before any subsystems are installed so that they can be configured with ECC subsystem certificates.
  • The CA profile pages can process ECC certificate requests, but they cannot generate ECC keys. Some of the profile forms, like manual user certificates, then cannot be used for ECC certificates. In those cases, a different or custom profile needs to be used, and certificate requests have to be generated using certutil.
For a CA to issue ECC certificates, the CA must be configured with an ECC CA signing certificate. This is best done by loading an ECC PKCS#11 module before the CA is installed, and then configuring the CA using ECC keys.


A CA with an ECC CA signing certificate can issue both ECC and RSA certificates. A CA with an RSA CA signing certificate can only issue RSA certificates.
Only the CA signing certificate is required; if for support purposes it is better to use RSA client certificates with the CA, simply delete the ECC subsystem certificates (except for the signing certificate) and replace them with RSA certificates.
For more information on ECC, see RFC 4492, Section 5.6.1, Table 2.