Further X25519 cipher support

[iFergal]

The Matter codex table in signify-ts only supports X25519_Cipher_Seed and X25519_Cipher_Salt.

If it's OK, I'd like to add the other 18 or so - X25519_Cipher_L0 -> X25519_Cipher_QB2_Big_L2 [encrypter.ts, decrypter.ts, cipher.ts, matter.ts] so we can sign arbitrary data. (e.g. for KERI ESSR from Signify)

My only question here is what class Decrypter._x25519 should return for these codecs - just Matter?

[SmithSamuelM]

Those codes were added originally to support key managmeent not for generic encryption.
The CESR 2.0 code table (see WebOfTrust/keripy#612) already encludes new codes for generic encryption using sealed box. These allow variable length encryptions

|   `4C`     | X25519 sealed box cipher bytes of sniffable plaintext lead size 0 |      4      |      2        |            |
|   `5C`     | X25519 sealed box cipher bytes of sniffable plaintext lead size 1 |      4      |      2        |            |
|   `6C`     | X25519 sealed box cipher bytes of sniffable plaintext lead size 2 |      4      |      2        |            |
|   `7AAC`   | X25519 sealed box cipher bytes of sniffable plaintext big lead size 0 |      8      |      4        |            |
|   `8AAC`   | X25519 sealed box cipher bytes of sniffable plaintext big lead size 1 |      8      |      4        |            |
|   `9AAC`   | X25519 sealed box cipher bytes of sniffable plaintext big lead size 2 |      8      |      4        |            |
|   `4D`     | X25519 sealed box cipher bytes of QB64 plaintext lead size 0 |      4      |      2        |            |
|   `5D`     | X25519 sealed box cipher bytes of QB64 plaintext lead size 1 |      4      |      2        |            |
|   `6D`     | X25519 sealed box cipher bytes of QB64 plaintext lead size 2 |      4      |      2        |            |
|   `7AAD`   | X25519 sealed box cipher bytes of QB64 plaintext big lead size 0 |      8      |      4        |            |
|   `8AAD`   | X25519 sealed box cipher bytes of QB64 plaintext big lead size 1 |      8      |      4        |            |
|   `9AAD`   | X25519 sealed box cipher bytes of QB64 plaintext big lead size 2 |      8      |      4        |            |
|   `4E`     | X25519 sealed box cipher bytes of QB2 plaintext lead size 0 |      4      |      2        |            |
|   `5E`     | X25519 sealed box cipher bytes of QB2 plaintext lead size 1 |      4      |      2        |            |
|   `6E`     | X25519 sealed box cipher bytes of QB2 plaintext lead size 2 |      4      |      2        |            |
|   `7AAE`   | X25519 sealed box cipher bytes of QB2 plaintext big lead size 0 |      8      |      4        |            |
|   `8AAE`   | X25519 sealed box cipher bytes of QB2 plaintext big lead size 1 |      8      |      4        |            |
|   `9AAE`   | X25519 sealed box cipher bytes of QB2 plaintext big lead size 2 |      8      |      4        |            |

[SmithSamuelM]

The Encrypter and Decrypter Classes will need to be updated to support the new codes

[iFergal]

Ah okay they came recently for CESR 2.0 - so they just didn't reach Signify-TS yet. I can create a PR this week to add support - thanks!

[iFergal]

@SmithSamuelM Do we need a new subclass of Matter to hold plaintexts after decrypting, or Matter is enough?

[SmithSamuelM]

Matter would not do any decrypting. So you would need the decrypter sub class or the like. All Matter does is handle the conversions between the three formats, Text (QB64), Binary (QB2), and Raw (Code, Raw) using the code tables. Matter enables the primitive to be ser/des by a generator/parser.

[iFergal]

@SmithSamuelM I mean in Decrypter.ts - what class _x25519 should return after decrypting;

For instance, right now if a X25519_Cipher_Salt is decrypted, we return a Salter instance and for X25519_Cipher_Seed, a Signer instance - https://github.com/WebOfTrust/signify-ts/blob/development/src/keri/core/decrypter.ts#L72

[SmithSamuelM]

for these variable length codes what will likely be returned are Bexter for the B64 encryptions and two new classes yet to be created that might be called Texter or Byter for arbitrary length bytestrings of text. and a new class for arbitrary length CESR Streamns. Name TBD.