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labs%2FLabDiffieHellman/diffie_hellman.jl

+function encode(message::String)
+    num = zero(BigInt)
+    for byte in reverse(Vector{UInt8}(message))
+        num <<= 8
+        num |= byte
+    end
+    return num
+end
+
+function decode(num::BigInt)
+    message = UInt8[]
+    while !iszero(num)
+        push!(message, convert(UInt8, num & typemax(UInt8)))
+        num >>= 8
+    end
+    return String(message)
+end
+
+@assert decode(encode("Hello world")) == "Hello world"
+
+decrypt(encrypted::BigInt, key::BigInt) = decode(encrypted - key)
+
+encrypt(message::String, key::BigInt) = encode(message) + key
+
+key = encode("key")
+
+@assert decrypt(encrypt("Hello world", key), key) == "Hello world"