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This is a text delivery system that someone can utilize to securely send shared secrets or passwords or even just arbitrary text to someone else.

The system tries to minimize the attack surface on the secrets by encrypting data at rest with a UUID that isn't stored on the system, and the UUID is only provided to the system by a user requesting the data associated with it, and when retrieving the data it is deleted as part of the same database query.

Goals

Maintain project simplicity while also securely handling secrets with reversible encryption.

How?

When an entry is created, it gets a Version 4 UUID generated as a unique key to find it later.

The UUID is then used as a key for PostgreSQLs pgp_sym_encrypt* function to encrypt the actual secret data.

But we don't want to store the decryption key right next to the data, so to mask it from the database, we pass the UUID, along with a salt, to PostgreSQLs hmac* function and store the result as our lookup key.

By doing things this way, we don't have the decryption key for any entry unless a request from a user provides it to us, we then pass it to hmac again to find an entry that matches the same key hash, and finally using the UUID as a key, we decrypt the payload field and return it to the requesting client.

Security

In an ideal world to transmit a secret to someone is to have already established a public/private key pair with them, then it is trivial to just encrypt and sign the data and send it over any medium, but in reality, very few people have those or even the knowledge how to use them (securely).

The attack surface on the shared secrets in this system should only be around submission and retrieval of the secrets since we have to work with them in plain text.

Our biggest vulnerability is unnoticed front end replacement/hijack while the system is in active use.

Database dump/theft is a low priority problem since you need the UUID to decrypt the payload field.

A plausible attack scenario is if an attacker can get a database backup and the request/ticket between the provider and user to get the UUID and what system that secret is for.

But then you'd have bigger issues to think about.

Database

The front end application accesses the database with a very restricted user, it only has execute permission on two stored procedures, nothing else.

It works because those functions are defined with a security definer* flag which means that when they are executed, they run with the permission of their owner, which does have more permissions.

Doing this ensures that front end bugs or exploits should not be able to attack or dump the back end database.

Website

The website is written in Go, it is written to be simple and robust as possible, the majority of the code is for handling errors gracefully and templating.

Wrapping

The codebase is built in a way that lets you make your own program that hooks into the request handler with RegisterRequestHandler et al.

The purpose is to allow templating, translation and even injection of features without modifying the upstream code itself.

Database creation

Run the following SQL with a superuser account before running any migration scripts.

create user password_frontend noinherit;
create role password_owner_role;
create database passwords WITH owner = password_owner_role template = template0 lc_collate = 'C' lc_ctype = 'C';

And then add a corresponding entry to pg_hba.conf. Example:

host passwords password_frontend ::1/128 trust

Note that there is no need to have multiple databases if you intend to run multiple instances, just use a different site secret in the config file.

References

* https://www.postgresql.org/docs/current/pgcrypto.html
** https://www.postgresql.org/docs/current/sql-createfunction.html