Add support to single line private keys on decryptionPvk

[jonathansamines]

Is your feature request related to a problem? Please describe.
No

Describe the solution you'd like
Would be nice if decryptionPvk could be specified as a single line private key just as privateKey can be specified in a singleline.

Describe alternatives you've considered
Not applicable

[markstos]

@jonathansamines You are welcome to submit a PR for this. Note that the first attempt to implement single-line-keys failed. Anyone implementing this should review what happened last time and what the solution was to make sure the same problem is not repeated here:

7e2de2d (scroll for discusson about the regression).

[jonathansamines]

Hey @markstos I looked into 7e2de2d and looks like #423 used a different implementation (currently in use for privateKey) which seem to have solved the original problem. Would the implementation on decryptionPvk be different than the one applied to privateKey?

[markstos]

@jonathansamines if the header and footers are the same, I presume the solution would be identical.