Plugin cipher & Value of a field

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1

Hello,

I am trying to use the value of a field, but I do not know why, I have the impression that the cipher plugin cannot read it. Could you help me figure out what's wrong please?

Below, I stored the value of "algorithm" in "[@metadata] [algorithm]" :

OK :

input { stdin { } }

filter {

  mutate {
    add_field => { "[@metadata][encrypted]" => "gKHInKhQooaPgF7m99B465HN4Wi5+ESCjq5LTc69h/I5+/fSsEbxGjk0NpiNrpH8" }
  }

  cipher {
    algorithm => "aes-256-cbc"
      iv_random_length => 16
      key => "12345678901234567890123456789012"
      key_size => 32
      mode => "decrypt"
      source => "[@metadata][encrypted]"
      target => "[@metadata][decrypted]"
  }
}

output { stdout { codec => rubydebug { metadata => true } } }

NOT OK : :slightly_frowning_face:

input { stdin { } }

filter {

  mutate {
    add_field => { 
    "[@metadata][encrypted]" => "gKHInKhQooaPgF7m99B465HN4Wi5+ESCjq5LTc69h/I5+/fSsEbxGjk0NpiNrpH8" 
    "[@metadata][algorithm]" => "aes-256-cbc"
    }
  }

  cipher {
    algorithm => "%{[@metadata][algorithm]}"
      iv_random_length => 16
      key => "12345678901234567890123456789012"
      key_size => 32
      mode => "decrypt"
      source => "[@metadata][encrypted]"
      target => "[@metadata][decrypted]"
  }
}

output { stdout { codec => rubydebug { metadata => true } } }

Thank you so much,

Florent

2

[ERROR] 2020-06-11 15:14:22.767 [[main]-pipeline-manager] javapipeline - Pipeline aborted due to error {:pipeline_id=>"main", :exception=>#<OpenSSL::Cipher::CipherError: unsupported cipher algorithm (%{[@METADATA][ALGORITHM]}/CBC/PKCS5Padding)>

3

The cipher filter does not sprintf the algorithm. It just uses the literal value.

4

What do you mean ?

I must write a "string" directly, and that I cannot use the value of a field ?

5

That is correct. A reference to a field like

algorithm => "%{[@metadata][algorithm]}"

is called a sprintf reference, and the filter or output would resolve it by calling a method called sprintf. That is typically done on fields that the plugin is setting, not inputs to the plugin.

6

OK !

I want to use cipher plugin more than once in my pipeline, and I don't want to write "algorithm / key / iv" every time. I wanted to centralize these parameters at the beginning of the file.

I feel like I can't do it, can I ?
Do you have another idea to avoid duplicating all these parameters throughout the file?

7

No, I cannot think of a way to avoid the duplication.

8

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