Document extensions to FROST

Also makes misc other doc corrections.

docs/cryptography/FROST.md

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+# FROST
+
+Serai implements [FROST](https://eprint.iacr.org/2020/852), as specified in
+[draft-irtf-cfrg-frost-11](https://datatracker.ietf.org/doc/draft-irtf-cfrg-frost/).
+
+### Modularity
+
+In order to support other algorithms which decompose to Schnorr, our FROST
+implementation is generic, able to run any algorithm satisfying its `Algorithm`
+trait. With these algorithms, there's frequently a requirement for further
+transcripting than what FROST expects. Accordingly, the transcript format is
+also modular so formats which aren't naive like the IETF's can be used.
+
+### Extensions
+
+In order to support algorithms which require their nonces be represented across
+multiple generators, FROST supports providing a nonce's commitments across
+multiple generators. In order to ensure their correctness,
+[CP93's Discrete Log Equality Proof](https://chaum.com/wp-content/uploads/2021/12/Wallet_Databases.pdf)
+is used. `2 * (n - 1)` proofs are included, since FROST nonces are binomial.
+Each pair of proofs prove discrete log equality between the first pair of
+commitments and each sequential pair. In the future, a single pair of DLEq
+proofs, proving for all generators, may be provided.
+
+As some algorithms require multiple nonces, effectively including multiple
+Schnorr signatures within one signature, the library also supports providing
+multiple nonces. The second component of a FROST nonce is intended to be
+multiplied by a per-participant binding factor to ensure the security of FROST.
+When additional nonces are used, this is actually a per-nonce per-participant
+binding factor.
+
+Finally, to support additive offset signing schemes (accounts, stealth
+addresses, randomization), it's possible to specify a scalar offset for keys.
+The public key signed for is also offset by this value. During the signing
+process, the offset is explicitly transcripted. Then, the offset is divided by
+`p`, the amount of participating signers, and each signer adds it to their
+post-interpolation key share.