88 lines
3.9 KiB
Markdown
88 lines
3.9 KiB
Markdown
# Schema and Encryption
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This document explains how the schema on the QR-Code is built and how it's encrypted.
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## Encryption
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OffPass uses **AES-256 CBC** as encrpytion. The key is calculated by the **Argon2id** hash algorithm.
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### Passphrase
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The passphrase is the actual key which is used for encrpytion. But we don't use your entered master password directly.
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We append a salt, which is a random sequence of characters, to your passphrase and then we hash it with `Argon2i` about 25 times. This gives use an output like this: `29dbf5392f13f36d7e9509b1a5c9add0d6a8e2625b5e84ab4d1df8da6063625d`.
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This value will be used as encryption key, not your plain password.
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The creation of such a hash takes about **more then one second**.
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Attackers are using password dictionaries with millions of passwords.
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Creating such a hash for each password in there would take **forever**.
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## QR-Code schema
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### Plain
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```txt
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Type_Indicator:IV:Salt:Encrypted_Content
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Example:
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op1:jI49Az0M1337leet:uZNqq901:YhSRA+nTiZxNfxUIhiJBSsPLTkACMRkbPbLtVbtUnGh3AKJkvQfXWitSUWNq83YjSuKqK64SbB+DygCPxkx6sJ9U0FsO3Waqb3tYn0JRQdEak9INiWx06WQeLsTQcoG2pibOhOZlyiHtZmBj+Ul//lIdYRnmdRgsxYlcYOthiIY=
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```
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An OffPass QR-Code must follow this data schema or else OffPass wouldn't be able to read it.
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**The following examples shows data after decryption.**
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```txt
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title|username|password|email|website_url|(custom1)data1|(custom2)data2
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```
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Two examples:
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```txt
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Main Steam Account|mondei1|super_secret_example123|info@example.de|https://store.steampowered.com/login/|(2fa_b)R1337|()Foo question%Bar awnser
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ProtonMail||mail_pw123|klier.nicolas@protonmail.com||
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```
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### Custom/Optional fields
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You can either define your own custom fields or use optional fields, which OffPass treats differently.
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List of optional fields:
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* `2fa` - Two factor authentication secret that starts like otpauth://totp/...
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* `2fa_b` - Backup codes for two factor authentication
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* `email_b` - Backup email address
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* `()QUESTION%AWNSER` - Security question with it's awnser. **Content inside the brackets has to be empty!**
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### Compression
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It is possible to compress QR-Codes. Instead of writing all data to the QR-Code you can write random strings (=key) to it.
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OffPass itself holds a database of those random strings and the corresponding encrypted value.
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The program generates a `session key` (fixed length of 10 characters) which is unique for each QR-Code.
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This session key is stored on inside the encrypted data field and is used to decrypt the raw values in database.
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**Not even If someone stells your database he wouldn't be able to read your compressed strings.**
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The compression key is stored like that: `§key`, the decryption key is stored like that: `%decryption_key%` always at the beginning.
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Please keep in mind that OffPass prevents you from compressing your title, password and username in case you lose
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access to your compression database.
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Eexample:
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```txt
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%session_key%§xa|mondei1|passwords_not2134|email_too@example.com|§q|(§a)§gh|(uncompressed)value
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-> %uI5Np98jAz%Google|mondei1|passwords_not2134|email_either@example.com|https://accounts.google.com|(2fa_backup)245131,...|(uncompressed)value
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```
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This can has two advantages:
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* An attacker can't read compressed values If he is able to decrypt a QR-Code (he would need the database)
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* You can get more data on one QR-Code
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But one disadvantage:
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* **If you lose access to the compression database, you also lose access to those compressed values. But not to your password.**
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### Reserved characters
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These characters are reserved and cannot be used in any fields: `|%§`
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### Type indicator
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OffPass will first look if the scanned QR-Code is actually an OffPass QR-Code. This is done by checking the first three charcters:
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```txt
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op1:...
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```
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This `op1:` tells the program that this is actully a OffPass QR-Code and which version. If this is not present, OffPass will abort further steps and notify the user that this is not an OffPass QR-Code. |