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jeffdecola / my-go-tools

git clone https://source.community/jeffdecola/my-go-tools.git

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/cryptography-tools/decryptfile/ (develop)

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📁 test/

📄 README.md

📄 decryptfile.go

📄 decryptfile_test.go

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[1]._

1: encryptfile

Table of Contents,

- OVERVIEW[1]

1: OVERVIEW

- STEP 1 - CREATE A HASH KEY[1]

- STEP 2 - DECRYPT FILE WITH 32 BYTE HASH KEY[2]

- PREREQUISITES[3]

- RUN[4]

- TEST[5]

- INSTALL[6]

- USAGE[7]

- -h[8]

- -v[9]

- -i string, -o string[10]

- -paraphrasefile string[11]

- -debug[12]

1: STEP 1 - CREATE A HASH KEY

2: STEP 2 - DECRYPT FILE WITH 32 BYTE HASH KEY

10: -i string, -o string

11: -paraphrasefile string

12: -debug

Documentation and references,

- Use my other tool

encryptfile[1] to encrypt * Refer to my aes-256-gcm[2] example in `my-go-examples` repo on how I did the decryption.

1: encryptfile

2: aes-256-gcm

- This repos

github webpage[1] _built with concourse[2]_

1: github webpage

2: 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[1] package.

1: crypto/aes

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[1] package.

1: crypto/md5

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[1] Refer to that example for a complete description.

1: aes-256-gcm

This illustration may help,

IMAGE - decryptfile - IMAGE[1]

1: IMAGE - decryptfile - IMAGE

PREREQUISITES

I used the following language,

- go[1]

1: 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[1].

1: run.sh

To run decryptfile.go[1] from the command line,

1: decryptfile.go

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[1].

1: 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

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