API for Validating Crypto Parameters

Hi All,

Is there any interest in providing APIs to validate parameters?

One of the things I try and teach my guys is that they must validate
cryptographic parameters; and they cannot apply a secret if validation
fails. Unvalidated keys could have flaws that allow for recovery of
the secret. For example, if an RSA public key does not validate, then
it should not be used to transport a secret.

GnuPG is a somewhat special case since its key pair is composed of
Lim-Lee primes. In this case, we can apply a "small prime" test; but
not a "strong prime" test.

Taking both standard practices and GnuPG into consideration, I believe
that means the API should accept a level for validation. Arbitrarily,
levels should probably follow the model set by certificate classes (1
= low, N = high), so a Level 0 would mean no validation; Level 1
validation would perform the small prime test; Level 2 would perform
the strong prime test (plus level 1), Level 3 could provide the tests
that take prolonged time (plus Level 2).

Its probably worth mentioning that local keys should be validated too
- for example, after loading a private key from a key store. So tests
like Jacobi and Miller-Rabin are also of interest.

Its common to offer validation and levels in other libraries. For
example, the Crypto++ library allows a developer to validate an object
and specify a level

    level    denotes the level of thoroughness: 0 - using this object
won't cause
    a crash or exception (rng is ignored) 1 - this object will probably function
    (encrypt, sign, etc.) correctly (but may not check for weak keys and such)
    2 - make sure this object will function correctly, and do
reasonable security
    checks 3 - do checks that may take a long time

Offering validation is consistent with the low level API that is
taking shape with the WebCrypto API.

Finally, other components, such as JOSE (JSON Web Algorithms (JWA),
JSON Web Encryption (JWE), JSON Web Key (JWK), and JSON Web Signature
(JWS)) does not even mention parameter validation. Someone has to do
it, and it appears others are expecting someone else to do it. This is
the Bystander Effect, and its a known problem in Security Engineering
(cf, Gutmann's Engineering Security, p. 82).


Received on Thursday, 30 May 2013 02:22:43 UTC