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quangtran's avatar
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Nov 28, 2022

use irule to sign data using sha256

Hello everyone, I have a request like this: HTTP REQUEST - header POST /login HTTP1/1 Host: xxxxxx <some other fields> - Body: <data> ----> f5 receives and uses Irule to modify the HTTP REQUE...
  • Kai_Wilke's avatar
    Dec 01, 2022

    Hi Quangtran,

    do you want to calculate the HMAC-checksum for the entire POST-data (Scenario 1) or just the "data" value itself (Scenario 2)?

    Scenario 1:

    hmac-sha256( the received POST string as-is including outer curly braces )

    Scenario 2:

    hmac-sha256( FdQZxoYBLPCgv2VPzdiUDA2Xj9KIJ\/I4BSzViIp\/CG\/ktrcdtXGYXQzGaa71R )

    The quickly code iRule below uses Scenario 1 as input for HMAC calculation. The iRule uses 4 logical steps to read the payload, calculate the checksum, define the new payload and finally insert the new payload to the HTTP request before its getting forwarded to your backend. Every single step could be easily adjusted based on your needs...


    when RULE_INIT {
    	# Define global configuration options
    	set static::max_payload_size "1048576" 		;# Limiter for maximum HTTP payload size in bytes
    	set static::hmac_key "Hello World!"			;# Secrect for HMAC signing
    when HTTP_REQUEST {
    	# Check if HTTP request contains any HTTP payload and if its size does not exceed our limits...
    	if { ( [string tolower [HTTP::path]] equals "/login" )
    	 and ( [HTTP::method] equals "POST" )
    	 and ( [HTTP::header value "Content-Length"] ne "" )
    	 and ( [HTTP::header value "Content-Length"] < $static::max_payload_size ) } then {
    		# Collect the HTTP payload and trigger HTTP_REQUEST_DATA event
    		HTTP::collect [HTTP::header value "Content-Length"]
    	# Define the input used for HMAC signing
    	set temp(hmac_input) [HTTP::payload]
    	# Compute the HMAC checksum for the input using our secret key
    	set temp(hmac_output) [b64encode [CRYPTO::sign -alg hmac-sha256 -key $static::hmac_key $temp(hmac_input)]]
    	# Contruct the new payload
    	set temp(new_payload) "[string trimright [HTTP::payload] "\}"],\"hashsha256\":\"$temp(hmac_output)\"\}"
    	# Replace the payload	
    	HTTP::payload replace 0 [HTTP::payload length] $temp(new_payload)
    	unset -nocomplain temp


    At later stage we may or may not combine those 4 logical steps into a single syntax line, to reduce processing overhead to a minimum.. 😉


    	# Replace the payload with HMAC signed payload...
    	HTTP::payload replace 0 [HTTP::payload length] "[string trimright [HTTP::payload] "\}"],\"hashsha256\":\"[b64encode [CRYPTO::sign -alg hmac-sha256 -key $static::hmac_key [HTTP::payload]]]\"\}"


    Cheers, Kai