feature: add pkcs #1 I2OSP & OS2IP

Author: NegaScout

benchmarks/utils.jl

@@ -0,0 +1,14 @@
+using ToyPublicKeys
+using BenchmarkTools
+using Random
+
+test_for_bitsizes = [1024, 2048, 4096]
+for bitsize in test_for_bitsizes
+    Random.seed!(42)
+    n = rand(big"2" << bitsize: big"2" << (bitsize + 1))
+    println("Benchmarking ToyPublicKeys.I2OSP for bitsize $bitsize")
+    display(@benchmark ToyPublicKeys.I2OSP($n))
+    str = ToyPublicKeys.I2OSP(n)
+    println("Benchmarking ToyPublicKeys.OS2IP for bitsize $bitsize")
+    display(@benchmark ToyPublicKeys.OS2IP($str))
+end

src/ToyPublicKeys.jl

@@ -3,6 +3,7 @@ module ToyPublicKeys
 include("utils/primes.jl")
 include("utils/random.jl")
 include("utils/number_theory.jl")
+include("utils/string.jl")
 include("padding/pkcs_1_v1_5.jl")
 include("rsa.jl")
 include("dh.jl")

src/utils/string.jl

@@ -0,0 +1,26 @@
+function I2OSP(x::BigInt)
+    return I2OSP(x, Base.GMP.MPZ.sizeinbase(x, 16))
+end
+
+function I2OSP(x::BigInt, xLen::Integer)
+    xLen |> isodd && (xLen += 1)
+    base_size = Base.GMP.MPZ.sizeinbase(x, 16)
+    base_size > xLen && throw(error("integer too big for xLen"))
+    buf = zeros(UInt8, xLen)
+    fill!(buf, '0')
+    buf_ptr = pointer(buf)
+    Base.GMP.MPZ.get_str!(buf_ptr + xLen - base_size, 16, x)
+    _buf = String(buf) |> uppercase
+    it = Iterators.Stateful(_buf)
+    part = Base.Iterators.partition(it, 2)
+    return join(map(join, part), ':')
+end
+
+function OS2IP(x::String)
+    # use Cstring instead..?
+    buf = replace(x, ":" => "") |> lowercase |> Vector{UInt8}
+    push!(buf, 0)
+    target = BigInt(0)
+    Base.GMP.MPZ.set_str!(target, pointer(buf), 16) == 0 || throw(error("string not valid base 16"))
+    return target
+end

test/runtests.jl

@@ -4,3 +4,4 @@ using Test
 include("rsa.jl")
 include("dh.jl")
 include("padding.jl")
+include("utils.jl")

test/utils.jl

@@ -0,0 +1,15 @@
+@testset "I2OSP" begin
+    b = big"255"
+    @test b |> ToyPublicKeys.I2OSP == "FF"
+    @test b |> x -> ToyPublicKeys.I2OSP(x, 3) == "00:FF"
+end
+
+@testset "OS2IP" begin
+    b = "FF"
+    @test b |> ToyPublicKeys.OS2IP == big"255"
+end
+
+@testset "I2OSP |> OS2IP" begin
+    b = big"255"
+    @test b |> ToyPublicKeys.I2OSP |> ToyPublicKeys.OS2IP == b
+end