Investigate the applicability of PURB to the exchange encryption

[cipriancraciun]

See the following sources:

• https://en.wikipedia.org/wiki/PURB_(cryptography)
• https://github.com/covert-encryption/covert/blob/main/docs/Specification.md
• https://github.com/covert-encryption/covert/blob/main/docs/Rationale.md
• https://www.kryptor.co.uk/specification

It mainly boils down to two orthogonal principles:

• the padding scheme shouldn't leak information about the payload;
• the whole encryption output (including any headers) should be indistinguishable from purely random data;

[hakavlad]

See also https://github.com/hakavlad/tird/blob/main/docs/SPECIFICATION.md

Padding is not yet discribed in the spec. The principle is as follows: a part of the Argon2 tag is converted to int and defines the total size of the paddings. The other part of the tag defines the proportions between the left and right parts of the paddings. The ciphertext is located between the left and right parts of the paddings. The size of the paddings is not saved in the header. This scheme hides not only the size but also the location of the ciphertext in the encrypted file.

Could you review this, please? What do you think about such scheme?

[cipriancraciun]

See also https://github.com/hakavlad/tird/blob/main/docs/SPECIFICATION.md

Could you review this, please? What do you think about such scheme?

I think I'll rather open a discussion on your project, because I think I have more questions with regard your specification that don't pertain strictly to the padding.

For the purpose of my project, I'll note that your padding has the following properties:

• it seems it is independent on the actual encrypted file; (perhaps dependent as a percentage of it?)
• the amount seems to be dependent on the encryption keys and the salt/nonce;
• it is applied both at the beginning and at the end (in different amounts) of the cipher text;

[hakavlad]

it seems it is independent on the actual encrypted file

It depends on the key, the size of the ciphertext, and the user-defined maximum padding percentage (20% by default).

Thanks.

[cipriancraciun]

I think I'll rather open a discussion on your project, because I think I have more questions with regard your specification that don't pertain strictly to the padding.

@hakavlad see my observations here: https://github.com/hakavlad/tird/discussions/17