Petar Popara wrote:

Bob,

Allow me few questions about DSA algorithm.

1. Is any key size supported (from 512 up to 2048 or 4096)?
All defined DSA sizes are support (as of when we wrote the code). That is from 512 to 1024, steps of 64. In practice everyone just used 1024 bits. This means the parameters are this size (not the actual private key) Here are the sizes of a DSA component:

These values may be shared my several people:
   p 512-1024 bits in steps of 64
   q 160 bits
   g  same order as p

These are per person:
   x (private key) less than q (order of 160 bits).
   y = g^x mod p (order of p).

2. Is output allways 40 bytes? And if it isn't then what it depends of? Key size?
DSA signatures are based on the size of 'q', which is always 160 bits (chosen to match the size of the SHA1 output). DSA produces to values:

r = (g^k mod p) mod q   and s = k^-(H(m) + xr) mod q

k is a random number generated for this signature, x is the private key, and H(m) is the SHA1 hash.
Thank you very much.

I would expect an update soon (if it is not already in progress) for DSA to support SHA128 and SHA256 . I would presume these
new 'DSA' algorithms will have a new mechanism number and new oids.

bob


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