feat(Keys_Incoming): Decrypt incoming ciphertext

[LHerskind]

Implementation in typescript

Following #5867 and #5899 we need to also be able to decode. This don't need to happen in a circuit so we simply do it in typescript. This should be able to take a look back at aztec-connect to see if it can get some information from there as it was also using AES.

Take into account #5901.

In aztec connect the ciphertext was called the viewing_key so should be helpful for finding the information.

Very close to #5902

[LHerskind]

As part of #5899 and #5867 there are typescript parts for encrypting and decryption these two.
We mainly need to deal with the combination of them into something that looks more like the encrypted log buffer that we have currently.

[LHerskind]

Related information in #5901 (comment).

[LHerskind]

This should be addressed along with #5901 to not have too many conflicts.

The l1_note_payload should be altered to take the eph_pk, header and body as outlined from the diagram, using the classes to handle decryption of those individually.

There should be a l1_note_payload::fromEncryptedBuffer function that does something along these lines:

  constructor(eph_public_key: Fr, header: EncryptedLogHeader, body: EncryptedLogBody) {}

  static fromEncryptedBuffer(data: Buffer, incomingViewingSecretKey: GrumpkinPrivateKey): L1NotePayload | undefined {
    const reader = BufferReader.asReader(data);
    const ephPK = Fr.fromBuffer(reader);
    const header = EncryptedLogHeader.fromCiphertext(data, incomingViewingSecretKey, ephPK);

    const appSecretKey = Fr.random();

    // slice data
    const body = EncryptedLogBody.fromCiphertext(data, appSecretKey, ephPK);

    return new L1NotePayload(ephPK, header, body);
  }

Similar changes should happen in the note processor to get this going.

Places to look:

• note_processor.ts
• l1_note_payload.ts
• client_execution_context.ts
  • The emitEncryptedLog should just take the raw array for tag and encrypted data
• private_context.nr
  • The emit_encrypted_log need to compute the header, body etc and compute the bytes that is to be emitted.
• logs.nr
  • The emit_encrypted_log oracle should be altered to take raw bytes and not return anything.

[LHerskind]

Was fixed in #6251 and #6411