feature that generate mac in ISO8583 Crypto PreProcessor UI based on specific fields

[mehrdad2000]

Hi
Would you please add feature that generate mac in ISO8583 Crypto PreProcessor UI based on specific fields.

E.g. fields: 0,2,11,12,47
concat these fields and based on these fields generate mac.

Any idea?
Thanks

[tilln]

Hi @mehrdad2000

Thanks for bringing this up.
I had not been aware there are messaging specs out there with MACs of only parts of the message.

Here is a work-around you can try:
Under your "ISO8583 Sampler", use a JSR223 PreProcessor with code like the below which should work assuming you include only "top-level" fields.

Note this avoids creating multiple instances of the MAC key and SecurityModule by caching a closure in a JMeter variable.

if (!vars.getObject('addMac')) {
    def macKey = new javax.crypto.spec.SecretKeySpec(
        org.jpos.iso.ISOUtil.hex2byte('1A1A1A1A1A1A1A1A1A1A1A1A1A1A1A1A'), 'ISO9797ALG3')
    def ssm = new nz.co.breakpoint.jmeter.iso8583.SecurityModule()

    vars.putObject('addMac', { sampler ->
        def msg = sampler.getRequest()
        def p = msg.getPackager()

        def bytes = [0,2,11,12,47].collect {
            p.getFieldPackager(it).pack(msg.getComponent(it))
        }.flatten() as byte[]

        sampler.addField('64', ssm.generateMAC(bytes, macKey, macKey.getAlgorithm()))
    })
}
vars.getObject('addMac').call(sampler)

Implementing this properly may be a bit more complicated to deal with the more general case of nested/subfields.

[mehrdad2000]

@tilln I try this but encounter with strange issue, I just want to concat these fields "data", but seems after packed add size of first field in start of "bytes", so i change this line from this:

            p.getFieldPackager(it).pack(msg.getComponent(it))

to this:

          msg.getComponent(it).getValue().getBytes()

after that field 11,37 are not same as what generate by sampler! all other part of message same!
seems not use of field 11,37 sampler value and instead generate new one!

FYI1: these fields generate by random function ${__Random(111111111111,999999999999,)}

FYI2: for debug issue add this line:

        log.info("bytes as text=${new String(bytes)}");  // Log bytes as text

[tilln]

@mehrdad2000

I have experienced this issue myself after upgrading to JMeter v5.6 where JMeter seems to evaluate function expressions such as ${__Random()} multiple times.
This apparently happens when a sampler property that contains a function is accessed more than once.

However, it is not an issue with this plugin.

The attached script demonstrates this with a single HTTP Sampler: jmeter-regression-v5.6.jmx.txt

Running this with -Lorg.apache.jmeter.functions=DEBUG will show that the function is invoked once with JMeter v5.5 but multiple times as of v5.6

I have not had time to investigate or log a JMeter bug so feel free to do that.

As a work-around you can assign the random function output to a JMeter variable first and put that variable in the sampler.

[tilln]

Before implementing this feature, I would need to understand what options to consider, such as list of input fields, how they are supposed to be combined to form the input bytes for the MAC calculation, e.g. packed by the packager or not, padded or not, with or without length and/or tag prefixes, etc.

As there are so many variations (and I don't know all of them yet) I think it may be easier to use some custom code as the above than to capture all the options in the "ISO8583 Crypto PreProcessor" configuration. Happy to make changes to expose additional methods to access the Sampler and/or Preprocessor instances/properties.

[mehrdad2000]

@tilln
1-ok thanks report jmeter issue here
2-I just need to use pure data of these fields without any padding or prefix etc.
3-i'm using 5.6.2 currently do you try 5.6.3? latest version of jmeter has this this issue?

[github-actions]

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