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JuliaLang / MbedTLS.jl

Wrapper around mbedtls
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Make CtrDrbg easier to use #207

Open chethega opened 5 years ago

chethega commented 5 years ago

Generating nonces is a very typical need. This is rather inconvenient with the currently existing exports. The issue came up when looking for a fix for https://github.com/GenieFramework/Genie.jl/issues/162 . Tangentially related https://github.com/JuliaLang/julia/issues/27614

What I'd like to see:

  1. Document-by-example proper safe usage, especially with respect to initialization and seeding.
  2. Use entropy as a default argument: CSPRNG = MbedTLS.CtrDrbg() does not give us a usable state. I am happy to report that direct calls to rand(CSPRNG, n) segfault instead of returning bad random. This is laudable: bad random is almost the worst possible behavior; a clean panic, or even a segfault is a much safer outcome. Exploitable memory corruption is the only worse thing one could possibly do.
  3. Either implement the Random interface correctly, or do not declare as a subtype of AbstractRNG. For comparison: 
    
julia> rng1 = Random.RandomDevice(); rng2 = MbedTLS.CtrDrbg(); MbedTLS.seed!(rng2, MbedTLS.Entropy());
julia> rand(rng1, Float32)
0.5747224f0

julia> rand(rng2, Float32) ERROR: ArgumentError: Sampler for this object is not defined

julia> rand(rng1, 2) 2-element Array{Float64,1}: 0.32157480543452466 0.032868961307404465

julia> rand(rng2, 2) 2-element Array{UInt8,1}: 0xc6 0x2f


4. Alternatively, don't export at all. People can look for other ways of generating secure random; better send them off than provide an option that is not misuse resistant.