Support - Decrypt App

Introduction

Decrypt is a simple iOS app for decrypting GPG-encrypted files using private keys. It allows you to read on your iPhone, files that have been encrypted on your Mac using GPG.

Workflow

Encrypt a file on your Mac using GPG
Transfer the encrypted file and your private key to your iPhone (using iCloud Drive, Dropbox, Google Drive, or any other cloud storage service)
Use this app to decrypt and view the file content on your iPhone

This is particularly useful for securely accessing sensitive documents on your iPhone without storing the decrypted content permanently on the device.

How to Use

Select the encrypted file you want to decrypt
Select your private key file
Enter the passphrase for your private key
Tap "Decrypt" to decrypt the file
The decrypted content will be displayed on screen

File Types

Encrypted files (.gpg)
Private key files (.asc)

About GPG

GPG (GNU Privacy Guard) is a widely used open-source implementation of the OpenPGP standard.

This app only supports asymmetric encryption (public/private key). It cannot decrypt files that were encrypted using symmetric encryption (password-only encryption).

MacOS Setup Instructions

Installing GPG on Mac OS

Install Homebrew if you don't have it:

/bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)"

Install GnuPG:
```
brew install gnupg
```

Creating and Exporting Keys

Generate a new GPG key:
```
gpg --default-preference-list "AES256 AES192 AES CAST5 SHA512 SHA256 SHA1 ZLIB BZIP2 ZIP Uncompressed" --full-generate-key
```
Important for iOS compatibility: --default-preference-list options are important in order to disable AEAD (Authenticated Encryption with Associated Data) as it's not supported at the moment by the library ObjectivePGP used in the iOS app

Choose the following options for instance:
- Kind of key: RSA and RSA
- Key size: 2048 bits
- Key validity: 0 = key does not expire
- Real name: Your Name
- Email address: your.email@example.com
- Comment: (optional)
- Passphrase: (required)
Export your private key:
```
gpg --export-secret-keys --armor your-email@example.com > private_key.asc
```
- Replace your-email@example.com with the email you used when creating the key
- Enter your passphrase when prompted
- The private key will be saved to private_key.asc
- Transfer this file to your iPhone for use with the app

Encrypting a file

gpg --encrypt --recipient your-email@example.com your_file.txt

This creates your_file.txt.gpg
Transfer this encrypted file to your iPhone for decryption with the app

Decrypting a file on Mac

gpg --decrypt your_file.txt.gpg > decrypted_file.txt

This will prompt for your private key passphrase
The decrypted content will be saved to decrypted_file.txt

Transferring files to iPhone

You can transfer the encrypted file and private key to your iPhone using various cloud storage services:

iCloud Drive
Dropbox
Google Drive
OneDrive
Or any other cloud storage service that provides iOS file access

Simply upload the files to your preferred service and access them through the Files app on your iPhone when using the GPG Decrypt app.

Security

All file operations use security-scoped resources
Passphrase is never stored
Files are copied to the app's documents directory for processing
Decrypted content is only displayed and not saved to the device
No persistent storage of sensitive information

Contact Support

If you need help, please contact us at:
decrypt@ach3d.com