decryptfile

README

decryptfile tool

decryptfile is a useful tool for decryptfile a file with AES-256 GCM (a 32-byte hash key) using the crypto/aes package. Works with encryptfile.

Table of Contents,

• OVERVIEW
  • STEP 1 - CREATE A HASH KEY
  • STEP 2 - DECRYPT FILE WITH 32 BYTE HASH KEY
• PREREQUISITES
• RUN
• TEST
• INSTALL
• USAGE
  • -h
  • -v
  • -i string, -o string
  • -paraphrasefile string
  • -debug

Documentation and references,

• Use my other tool encryptfile to encrypt
• Refer to my aes-256-gcm example in my-go-examples repo on how I did the decryption.
• This repos github webpage built with concourse

OVERVIEW

The Advanced Encryption Standard, or AES, is a symmetric block cipher chosen by the U.S. government to protect classified information and is implemented in software and hardware throughout the world to encrypt sensitive data.

We're going to use AES-256 GCM encryption from the standard go crypto/aes package.

STEP 1 - CREATE A HASH KEY

First you need a 32 byte key (AES-256). Instead of typing a 32 character in, lets make it simple by turning a simple paraphrase into a key. We will use the standard go crypto/md5 package.

hasher := md5.New()
hasher.Write([]byte(paraphrase))
hash := hex.EncodeToString(hasher.Sum(nil))

STEP 2 - DECRYPT FILE WITH 32 BYTE HASH KEY

The encryption was done using AES-256 GCM from my example aes-256-gcm Refer to that example for a complete description.

This illustration may help,

PREREQUISITES

I used the following language,

• go

You will need the following go packages,

go get -u -v github.com/sirupsen/logrus

RUN

The following steps are located in run.sh.

To run decryptfile.go from the command line,

go run . -i encrypted.txt -o output.txt
go run decryptfile.go -i encrypted.txt -o output.txt
go run decryptfile.go -i encrypted.txt -o output.txt -debug
go run decryptfile.go -i encrypted.txt -o output.txt -paraphrasefile paraphrase.txt
go run decryptfile.go -i encrypted.txt -o output.txt -paraphrasefile ~/.ssh/id_rsa

Use the paraphrase test.

TEST

The following steps are located in unit-tests.sh.

To create _test files,

gotests -w -all decryptfile.go

To unit test the code,

go test -cover ./... | tee test/test_coverage.txt
cat test/test_coverage.txt

INSTALL

Will place an executable in your go bin,

go install decryptfile.go

USAGE

decryptfile {-h|-v|-debug} -i [input file] -o [output file] -paraphrasefile [file]

-h

Help,

decryptfile -h

-v

Version,

decryptfile -v

-i string, -o string

Use a specific input file and output file`,

decryptfile -i encrypted.txt -o output.txt

-paraphrasefile string

Use a file as the paraphrase,

decryptfile -i encrypted.txt -o output.txt -paraphrasefile ~/.ssh/id_rsa

-debug

decryptfile -i encrypted.txt -o output.txt -debug