mvx-crypto-verification

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# MultiversX Crypto Verification — `self.crypto()` API Reference

Complete reference for hashing and signature verification in MultiversX smart contracts (SDK v0.64+).

## Hashing Functions

All hashing functions take `&ManagedBuffer` (or anything that borrows as `ManagedBuffer`) and return a fixed-size `ManagedByteArray`.

| Method | Return Type | Output Size | Use Case |
|--------|------------|-------------|----------|
| `.sha256(data)` | `ManagedByteArray<A, 32>` | 32 bytes | General purpose hashing, Merkle trees |
| `.keccak256(data)` | `ManagedByteArray<A, 32>` | 32 bytes | Ethereum compatibility, EIP-712 |
| `.ripemd160(data)` | `ManagedByteArray<A, 20>` | 20 bytes | Bitcoin address derivation (rare) |

```rust
// Hash a message
let message = ManagedBuffer::from("data to hash");
let hash: ManagedByteArray<Self::Api, 32> = self.crypto().sha256(&message);

// Hash for Ethereum compatibility
let eth_hash = self.crypto().keccak256(&abi_encoded_data);
```

## Signature Verification

### Critical Distinction: Panic vs Bool

**Panic-based** — Transaction fails immediately on invalid signature. No error handling possible. Use when invalid signature = unauthorized action.

**Bool-based** — Returns `true`/`false`. Contract continues execution. Use when you need graceful error handling or multiple verification attempts.

| Method | Returns | On Invalid Signature |
|--------|---------|---------------------|
| `verify_ed25519(key, message, signature)` | `()` | **Panics** — tx fails with "invalid signature" |
| `verify_bls(key, message, signature)` | `()` | **Panics** |
| `verify_secp256r1(key, message, signature)` | `()` | **Panics** |
| `verify_bls_signature_share(key, message, signature)` | `()` | **Panics** |
| `verify_bls_aggregated_signature(keys, message, signature)` | `()` | **Panics** |
| `verify_secp256k1(key, message, signature)` | `bool` | **Returns false** |
| `verify_custom_secp256k1(key, message, signature, hash_type)` | `bool` | **Returns false** |

### Method Signatures

```rust
// Panic-based (no return value)
fn verify_ed25519(
    &self,
    key: &ManagedBuffer<A>,       // 32-byte public key
    message: &ManagedBuffer<A>,   // arbitrary message
    signature: &ManagedBuffer<A>, // 64-byte signature
)

fn verify_bls(
    &self,
    key: &ManagedBuffer<A>,       // 96-byte BLS public key
    message: &ManagedBuffer<A>,
    signature: &ManagedBuffer<A>, // 48-byte BLS signature
)

fn verify_secp256r1(
    &self,
    key: &ManagedBuffer<A>,       // 33 or 65-byte public key
    message: &ManagedBuffer<A>,
    signature: &ManagedBuffer<A>,
)

fn verify_bls_signature_share(
    &self,
    key: &ManagedBuffer<A>,
    message: &ManagedBuffer<A>,
    signature: &ManagedBuffer<A>,
)

fn verify_bls_aggregated_signature(
    &self,
    keys: &ManagedVec<A, ManagedBuffer<A>>,  // list of BLS public keys
    message: &ManagedBuffer<A>,
    signature: &ManagedBuffer<A>,             // aggregated signature
)

// Bool-based
fn verify_secp256k1(
    &self,
    key: &ManagedBuffer<A>,
    message: &ManagedBuffer<A>,
    signature: &ManagedBuffer<A>,  // DER-encoded or raw (min 2 bytes)
) -> bool

fn verify_custom_secp256k1(
    &self,
    key: &ManagedBuffer<A>,
    message: &ManagedBuffer<A>,
    signature: &ManagedBuffer<A>,
    hash_type: MessageHashType,    // how the message was hashed
) -> bool
```

### MessageHashType Enum

Used with `verify_custom_secp256k1` to specify how the message was pre-hashed:

```rust
pub enum MessageHashType {
    ECDSAPlainMsg,      // Message is not hashed (raw)
    ECDSASha256,        // Message was SHA-256 hashed
    ECDSADoubleSha256,  // Message was double SHA-256 hashed (Bitcoin)
    ECDSAKeccak256,     // Message was Keccak-256 hashed (Ethereum)
    ECDSARipemd160,     // Message was RIPEMD-160 hashed
    ECDSABlake2b,       // Message was Blake2b hashed
}
```

### DER Signature Encoding

Convert raw (r, s) components to DER format for secp256k1:

```rust
fn encode_secp256k1_der_signature(
    &self,

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