# Logstash Fingerprint Plugin Target Unchanged
**URL:** https://discuss.elastic.co/t/logstash-fingerprint-plugin-target-unchanged/352247
**Category:** Logstash
**Created:** [February 1, 2024, 5:45am UTC](https://discuss.elastic.co/t/logstash-fingerprint-plugin-target-unchanged/352247 "2024-02-01T05:45:36Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@Cheese](https://discuss.elastic.co/u/Cheese)
#### Post date: [February 1, 2024, 5:45am UTC](https://discuss.elastic.co/t/logstash-fingerprint-plugin-target-unchanged/352247/1 "2024-02-01T05:45:36Z")
HI all,
Needing some help with using the Fingerprint plugin.
I use the fingerprint plugin to generate a SHA-1 signature using a base string and a key. My logstash config file is like so:
```auto
mutate {
add_field {
"signature" => ""
"signature_key" => XYZ
"base_string" => ABC&DEF&GHI
}
}
...
fingerprint {
ecs_compatibility => "disabled"
method => "SHA1"
key => "%{signature_key}"
source => ["%{base_string}"]
target => "signature"
add_field => { "sha_success" => "yay" }
}
...
output {
stdout { codec => rubydebug }
}
```
Upon inspection in the terminal when running the config file:
```auto
"signature" => ""
...
"sha_success" => "yay"
```
when I am expecting "signature" to be.. a signature.
Is there something wrong with how I am calling the fingerprint plugin?
EDIT: I am using Logstash 8.11.1, tested on Logstash 8.12 and same outcome
---
### Author:  [@leandrojmp](https://discuss.elastic.co/u/leandrojmp)
#### Post date: [February 1, 2024, 10:37am UTC](https://discuss.elastic.co/t/logstash-fingerprint-plugin-target-unchanged/352247/2 "2024-02-01T10:37:44Z")
> [@Cheese](#):
>
> ```auto
> fingerprint {
> ecs_compatibility => "disabled"
> method => "SHA1"
> key => "%{signature_key}"
> source => ["%{base_string}"]
> target => "signature"
> add_field => { "sha_success" => "yay" }
> }
>
> ```
The `source` option needs to be the field name.
> The name(s) of the source field(s) whose contents will be used to create the fingerprint.
So you should use it like this:
```auto
source => ["base_string"]
```
Also, I'm not sure that using `%{signature_key}` in the `key` option would get the value of the `signature_key` or use the literal value of `%{signature_key}` as the key, didn't look at the code to confirm, not every option in every filter will support sprintf of fields.
I would use the key directly in the filter to avoid any mistakes, you there is no need to create an empty `signature` field.
---
### Author:  [@Badger](https://discuss.elastic.co/u/Badger)
#### Post date: [February 1, 2024, 6:32pm UTC](https://discuss.elastic.co/t/logstash-fingerprint-plugin-target-unchanged/352247/3 "2024-02-01T18:32:19Z")
> [@Cheese](#):
>
> Is there something wrong with how I am calling the fingerprint plugin?
Yes. Adding to what Leandro said, the filter does not sprintf the value of the source option. It just [iterates over](https://github.com/logstash-plugins/logstash-filter-fingerprint/blob/97851b890b0237bcfb28fdab2ea0ff0820357129/lib/logstash/filters/fingerprint.rb) the members of the array. If no such field exists then the filter is a no-op.
It also does not sprintf the key option. But I would question why you are using the key option at all. Do you really need a message authentication code rather than a hash? A key is a shared secret that the receiver of the fingerprint can use to authenticate it. If you just need a hash then do not set the key option.
---
### Author:  [@Cheese](https://discuss.elastic.co/u/Cheese)
#### Post date: [February 1, 2024, 9:44pm UTC](https://discuss.elastic.co/t/logstash-fingerprint-plugin-target-unchanged/352247/4 "2024-02-01T21:44:30Z")
> [@Badger](#):
>
> It also does not sprintf the key option. But I would question why you are using the key option at all. Do you really need a message authentication code rather than a hash? A key is a shared secret that the receiver of the fingerprint can use to authenticate it. If you just need a hash then do not set the key option.
Hi all, thanks for the response 🙂 I was indeed using the source field incorrectly. For context I am trying to use OAUth1 to generate a SHA1 signature within Logstash
---
### Author:  [@system](https://discuss.elastic.co/u/system)
#### Post date: [February 29, 2024, 9:44pm UTC](https://discuss.elastic.co/t/logstash-fingerprint-plugin-target-unchanged/352247/5 "2024-02-29T21:44:44Z")
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