How to decrypt Jenkins 8mha values

That string is ansi-/ color-coded log output. To view the plain text version, you can utilize https://github.com/mmalecki/ansispan.So, the given String

    [8mha:AAAAaB+LCAAAAAAAAP9b85aBtbiIwTG/KF0vKzUvOzOvODlTryCnNB3I0ivPL8pOy8kv18vKT9JLzs8rzs9J1QuHCgaV5jlDhPzyS1IZIICRiYGhoohBKqM0pTg/D64Hh8ICAFt0h+h/AAAA[0m[Pipeline] { (prepare)    [8mha:AAAAaB+LCAAAAAAAAP9b85aBtbiIwTG/KF0vKzUvOzOvODlTryCnNB3I0ivPL8pOy8kv18vKT9JLzs8rzs9J1QuHCgaV5jlDhPzyS1IZIICRiYGhoohBKqM0pTg/D64Hh8ICAFt0h+h/AAAA[0m[Pipeline] }    [8mha:AAAAaB+LCAAAAAAAAP9b85aBtbiIwTG/KF0vKzUvOzOvODlTryCnNB3I0ivPL8pOy8kv18vKT9JLzs8rzs9J1QuHCgaV5jlDhPzyS1IZIICRiYGhoohBKqM0pTg/D64Hh8ICAFt0h+h/AAAA[0m[Pipeline] // stage    [8mha:AAAAaB+LCAAAAAAAAP9b85aBtbiIwTG/KF0vKzUvOzOvODlTryCnNB3I0ivPL8pOy8kv18vKT9JLzs8rzs9J1QuHCgaV5jlDhPzyS1IZIICRiYGhoohBKqM0pTg/D64Hh8ICAFt0h+h/AAAA[0m[Pipeline] stage    [8mha:AAAAaB+LCAAAAAAAAP9b85aBtbiIwTG/KF0vKzUvOzOvODlTryCnNB3I0ivPL8pOy8kv18vKT9JLzs8rzs9J1QuHCgaV5jlDhPzyS1IZIICRiYGhoohBKqM0pTg/D64Hh8ICAFt0h+h/AAAA[0m[Pipeline] { (deployApplication)    [8mha:AAAAaB+LCAAAAAAAAP9b85aBtbiIwTG/KF0vKzUvOzOvODlTryCnNB3I0ivPL8pOy8kv18vKT9JLzs8rzs9J1QuHCgaV5jlDhPzyS1IZIICRiYGhoohBKqM0pTg/D64Hh8ICAFt0h+h/AAAA[0m[Pipeline] }    [8mha:AAAAaB+LCAAAAAAAAP9b85aBtbiIwTG/KF0vKzUvOzOvODlTryCnNB3I0ivPL8pOy8kv18vKT9JLzs8rzs9J1QuHCgaV5jlDhPzyS1IZIICRiYGhoohBKqM0pTg/D64Hh8ICAFt0h+h/AAAA[0m[Pipeline] // stage

will result in

    [Pipeline] { (prepare)    [Pipeline] }    [Pipeline] // stage    [Pipeline] stage    [Pipeline] { (deployApplication)    [Pipeline] }    [Pipeline] // stage

https://github.com/LarrysGIT/Extract-Jenkins-Raw-Log/blob/master/README.md

Short answer here,

It's not encrypted, it still BASE64 string,

Example,

Started by user [8mha:////4H+H6gi+RzqRXgbuxDkiDNvJYq3pMCu17+YXxGOB+mHbAAAAlx+LCAAAAAAAAP9b85aBtbiIQTGjNKU4P08vOT+vOD8nVc83PyU1x6OyILUoJzMv2y+/JJUBAhiZGBgqihhk0NSjKDWzXb3RdlLBUSYGJk8GtpzUvPSSDB8G5tKinBIGIZ+sxLJE/ZzEvHT94JKizLx0a6BxUmjGOUNodHsLgAzWEgZu/dLi1CL9xJTczDwAj6GcLcAAAAA=[0madmin

Can be split to the following parts,

A string: Started by user

Preamber: \u001B[8mha:

Base64 string: ////4H+H6gi+RzqRXgbuxDkiDNvJYq3pMCu17+YXxGOB+mHbAAAAlx+LCAAAAAAAAP9b85aBtbiIQTGjNKU4P08vOT+vOD8nVc83PyU1x6OyILUoJzMv2y+/JJUBAhiZGBgqihhk0NSjKDWzXb3RdlLBUSYGJk8GtpzUvPSSDB8G5tKinBIGIZ+sxLJE/ZzEvHT94JKizLx0a6BxUmjGOUNodHsLgAzWEgZu/dLi1CL9xJTczDwAj6GcLcAAAAA=

Postamber: \u001B[0m

A string: admin

Convert the base64 string to bytes, trim the first 40 bytes (https://github.com/LarrysGIT/Extract-Jenkins-Raw-Log/issues/1) and save as .gz file. Now you can extract real content from the .gz file.

In this case, the content is type Java serialization data, version 5 following

¬í sr !hudson.console.ModelHyperlinkNote xr hudson.console.HyperlinkNote6=«±=’pÅ I lengthL urlt Ljava/lang/String;xr hudson.console.ConsoleNote xp t /user/admin