After reviewing the documentation I see this behavior mentioned - easy to miss. However I'd argue that this behavior is wrong, given that there is no context to potentially re-use with the single shot function.
Wouldn't it make more sense to simply treat a NULL pointer to key the same as passing a valid pointer, when key_len is 0, for the single-shot function? -- Jake Petroules Chief Technology Officer Petroules Corporation ยท www.petroules.com Email: [email protected] On Jul 26, 2013, at 8:46 AM, Stephen Henson via RT <[email protected]> wrote: > On Fri Jul 26 09:26:23 2013, [email protected] wrote: >> Hello, >> >> I've discovered a bug in OpenSSL HMAC handling -- when calling the >> HMAC() (http://www.openssl.org/docs/crypto/hmac.html) function, an >> incorrect result will be given if the `key` parameter is a NULL >> pointer, even when `key_len` is zero. Much easier to notice when >> you're not using null terminated strings/buffers. I would expect >> that the value of `key` would have no effect if `key_len` is 0 >> (CommonCrypto handles this fine). I have attached an example >> program demonstrating the problem. >> > > Passing "NULL" as the key has a special meaning to the OpenSSL APIs: it reuses > the existing HMAC key for the context. If there is no HMAC key previously set > the result is undefined. If you really want to use a zero length key set > key_len to zero and key to non-NULL. > > Steve. > -- > Dr Stephen N. Henson. OpenSSL project core developer. > Commercial tech support now available see: http://www.openssl.org
