BIP32-Ed25519

This crate implements BIP32 for Ed25519 according to the paper BIP32-Ed25519 Hierarchical Deterministic Keys over a Non-linear Keyspace:

Fork information

This crate contains some code copied from https://github.com/typed-io/rust-ed25519-bip32, especially:

The add_28_mul8() and add_256bits() functions.
Some parts of the public and private key derivation functions.

This crate deviates from the above project in the following ways:

Using RustCrypto libraries for SHA512, HMAC, and Curve25519 operations instead of cryptoxide. Rationale: the primary user of this library, the BitBox02 firmware, already includes RustCrypto dependencies, so reusing these does not grow the firmware binary size unnecessarily.
no_std - no dependency on std. There is a dependency on alloc, so an allocator is required.
Use of zeroize.
Better unit test coverage.

Table tests

In tests/table_test.rs, this implementation is tested to yield the same results as:

https://github.com/typed-io/rust-ed25519-bip32
Ledger's reference implementation, which showcases what their SDK's os_perso_derive_node_bip32_seed_key() function computes. Ledger uses this to derive e.g. Cardano keys.