How to convert an hex string into ascii string in Lua

Question

I have no knowledge at all about LUA and I'm trying to craft a small script for nginx.

I'm using the following library ( https://github.com/openresty/lua-resty-string ) to encrypt some data. Specifically I'm using the code for AES 256 CBC (SHA-512, salted) encryption and storing the hex-encoded encrypted string as shown in the example.

The issue now is that I need to get that hex string back to the decrypt method which expects an ASCII string.

This is an example of the encrypted hex string:

fdbcc47fe5825d49ac3429d4f8408fa4b6528dd99d938f122ee7f00ab71ae0c5c73d29d4f54ea1fbefe706b5dca04f6b6c6b8b96d9807ef58eaba07c6c6cefaf6ad8673b43a4e243fb2912fb4ff93de6488c4795ebb09ecd7a40b7c9dc2003be4ff93425d2d74688208fa4d2a8d22f32490666550f4b01340de708d7aa5bc8468d171da400f59fcff4e7d371d7ab9b48fdfde29aefc0af78b2f934927a7713994c1e8f9435067c851efc5d300405c74d

Answer 1

Just had to write one recently for pretty much same reason. Abuse gsub - capture each two chars and replace them with pre-calculated values from hexnumber->character map.

-- Needs to be only done once
local hex_to_char = {}
for idx = 0, 255 do
    hex_to_char[("%02X"):format(idx)] = string.char(idx)
    hex_to_char[("%02x"):format(idx)] = string.char(idx)
end

-- Sometime later
str = "fdbcc47fe5825d49ac3429d4f8408fa4b6528dd99d938f122ee7f00ab71ae0c5c73d29d4f54ea1fbefe706b5dca04f6b6c6b8b96d9807ef58eaba07c6c6cefaf6ad8673b43a4e243fb2912fb4ff93de6488c4795ebb09ecd7a40b7c9dc2003be4ff93425d2d74688208fa4d2a8d22f32490666550f4b01340de708d7aa5bc8468d171da400f59fcff4e7d371d7ab9b48fdfde29aefc0af78b2f934927a7713994c1e8f9435067c851efc5d300405c74d"
print(str:gsub("(..)", hex_to_char))