Released in 1997 and made popular by Edward Snowden and Glenn Greenwald, GnuPG (Gnu Privacy Guard) has a reputation as one of the most reliable and established encryption methods. A text file encrypted with the Gnu Privacy Guard ensures a secure and accessible password storage.
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Pro Can be easily integrated with other command-line tools
For example, I can run GITHUB_TOKEN=$(gpg -d GITHUB_TOKEN.gpg) some_tool
Pro Outstanding compatibility
GPG is standard on most operating systems, and is compatible with "too many to list". A GPG API is currently being developed for further integration.
Pro Free to use and modify
GPG does not use patented algorithms, so this service is free to use and modify without restrictions.
Pro Can be used with any system that understands text files
Text files are ubiquitous. They can be read across any modern platform and many obsolete one's.
Pro No dependencies
GnuPG does not depend on a reading program in order to be functional.
Pro Uses symmetric key encryption to ensure that emails are secure
Symmetric key encryption not only protects emails from unauthorized access, but it ensures that the sender and receiver are legitimate.