VRF RFC9381

https://docs.rs/vrf-rfc9381
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VRF-RFC9381 is a Rust implementation of Verifiable Random Functions as described in RFC9381,...
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### unwrap_or_else Example

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/error/type.VrfResult.html

Demonstrates the use of unwrap_or_else with both Ok and Err variants.

```rust
assert_eq!(Ok(2).unwrap_or_else(count), 2);
assert_eq!(Err("foo").unwrap_or_else(count), 3);
```

--------------------------------

### Verifier Implementations

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/trait.Verifier.html

Examples of Verifier trait implementations for different public key types and hash algorithms.

```APIDOC
### impl Verifier<Sha256> for EcVrfP256SswuPublicKey
Available on **crate features`ec` and `p256`** only.
#### type Proof = EcVrfProof

### impl Verifier<Sha256> for EcVrfP256TaiPublicKey
Available on **crate features`ec` and `p256`** only.
#### type Proof = EcVrfProof

### impl Verifier<Sha512> for EdVrfEdwards25519Ell2PublicKey
Available on **crate features`ec` and `edwards25519`** only.
#### type Proof = EdVrfProof

### impl Verifier<Sha512> for EdVrfEdwards25519TaiPublicKey
Available on **crate features`ec` and `edwards25519`** only.
#### type Proof = EdVrfProof
```

--------------------------------

### To ASCII Uppercase Example

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/struct.Ciphersuite.html

Converts a byte to its ASCII uppercase equivalent. Non-ASCII characters remain unchanged.

```rust
let lowercase_a = 97u8;

assert_eq!(65, lowercase_a.to_ascii_uppercase());
```

--------------------------------

### To ASCII Lowercase Example

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/struct.Ciphersuite.html

Converts a byte to its ASCII lowercase equivalent. Non-ASCII characters remain unchanged.

```rust
let uppercase_a = 65u8;

assert_eq!(97, uppercase_a.to_ascii_lowercase());
```

--------------------------------

### Unsafe unwrap_err_unchecked Example

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/error/type.VrfResult.html

Shows how to use unwrap_err_unchecked on an Err value. Calling this on an Ok is undefined behavior.

```rust
let x: Result<u32, &str> = Err("emergency failure");
assert_eq!(unsafe { x.unwrap_err_unchecked() }, "emergency failure");
```

--------------------------------

### Unsafe unwrap_unchecked Example

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/error/type.VrfResult.html

Shows how to use unwrap_unchecked on an Ok value. Calling this on an Err is undefined behavior.

```rust
let x: Result<u32, &str> = Ok(2);
assert_eq!(unsafe { x.unwrap_unchecked() }, 2);
```

--------------------------------

### ASCII Case-Insensitive Comparison Example

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/struct.Ciphersuite.html

Compares two byte values for ASCII case-insensitivity. This is equivalent to converting both to lowercase before comparison.

```rust
let lowercase_a = 97u8;
let uppercase_a = 65u8;

assert!(lowercase_a.eq_ignore_ascii_case(&uppercase_a));
```

--------------------------------

### Is ASCII Alphabetic Example

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/struct.Ciphersuite.html

Checks if a byte represents an ASCII alphabetic character (A-Z or a-z).

```rust
let uppercase_a = b'A';
let uppercase_g = b'G';
let a = b'a';
let g = b'g';
let zero = b'0';
let percent = b'%';
let space = b' ';
let lf = b'\n';
let esc = b'\x1b';

assert!(uppercase_a.is_ascii_alphabetic());
assert!(uppercase_g.is_ascii_alphabetic());
assert!(a.is_ascii_alphabetic());
assert!(g.is_ascii_alphabetic());
assert!(!zero.is_ascii_alphabetic());
assert!(!percent.is_ascii_alphabetic());
assert!(!space.is_ascii_alphabetic());
assert!(!lf.is_ascii_alphabetic());
assert!(!esc.is_ascii_alphabetic());
```

--------------------------------

### ASCII Check Example

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/struct.Ciphersuite.html

Checks if a byte value falls within the ASCII character range.

```rust
let ascii = 97u8;
let non_ascii = 150u8;

assert!(ascii.is_ascii());
assert!(!non_ascii.is_ascii());
```

--------------------------------

### Unwrap Ok Value (Basic Usage)

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/error/type.VrfResult.html

Use `unwrap()` to get the contained `Ok` value. This method will panic if the `Result` is an `Err`. It is generally discouraged in favor of safer error handling methods.

```Rust
let x: Result<u32, &str> = Ok(2);
assert_eq!(x.unwrap(), 2);
```

--------------------------------

### Collecting Results into a Vector (Success)

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/error/type.VrfResult.html

Demonstrates using `collect` on an iterator of Results, where all elements are Ok. This example checks for integer overflow.

```rust
let v = vec![1, 2];
let res: Result<Vec<u32>, &'static str> = v.iter().map(|x: &u32| 
    x.checked_add(1).ok_or("Overflow!")
).collect();
assert_eq!(res, Ok(vec![2, 3]));
```

--------------------------------

### Ciphersuite From<u8> Implementation

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/struct.Ciphersuite.html

Provides a way to create a Ciphersuite instance from a u8 value.

```APIDOC
## fn from(value: u8) -> Self

### Description
Converts to this type from the input type.

### Method
from

### Parameters
- `value`: The u8 value to convert from.

### Returns
A new Ciphersuite instance created from the u8 value.
```

--------------------------------

### Is ASCII Lowercase Example

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/struct.Ciphersuite.html

Checks if a byte represents an ASCII lowercase character (a-z).

```rust
let uppercase_a = b'A';
let uppercase_g = b'G';
let a = b'a';
let g = b'g';
let zero = b'0';
let percent = b'%';
let space = b' ';
let lf = b'\n';
let esc = b'\x1b';

assert!(!uppercase_a.is_ascii_lowercase());
assert!(!uppercase_g.is_ascii_lowercase());
assert!(a.is_ascii_lowercase());
assert!(g.is_ascii_lowercase());
assert!(!zero.is_ascii_lowercase());
assert!(!percent.is_ascii_lowercase());
assert!(!space.is_ascii_lowercase());
assert!(!lf.is_ascii_lowercase());
assert!(!esc.is_ascii_lowercase());
```

--------------------------------

### Is ASCII Uppercase Example

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/struct.Ciphersuite.html

Checks if a byte represents an ASCII uppercase character (A-Z).

```rust
let uppercase_a = b'A';
let uppercase_g = b'G';
let a = b'a';
let g = b'g';
let zero = b'0';
let percent = b'%';
let space = b' ';
let lf = b'\n';
let esc = b'\x1b';

assert!(uppercase_a.is_ascii_uppercase());
assert!(uppercase_g.is_ascii_uppercase());
assert!(!a.is_ascii_uppercase());
assert!(!g.is_ascii_uppercase());
assert!(!zero.is_ascii_uppercase());
assert!(!percent.is_ascii_uppercase());
assert!(!space.is_ascii_uppercase());
assert!(!lf.is_ascii_uppercase());
assert!(!esc.is_ascii_uppercase());
```

--------------------------------

### Ciphersuite Clone Implementation

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/struct.Ciphersuite.html

Provides methods for cloning and copying Ciphersuite instances.

```APIDOC
## fn clone(&self) -> Ciphersuite

### Description
Returns a duplicate of the value.

### Method
clone

### Parameters
- `self`: A reference to the Ciphersuite instance.

### Returns
A new Ciphersuite instance that is a duplicate of the original.
```

```APIDOC
## fn clone_from(&mut self, source: &Self)

### Description
Performs copy-assignment from `source`.

### Method
clone_from

### Parameters
- `self`: A mutable reference to the Ciphersuite instance to be updated.
- `source`: A reference to the source Ciphersuite instance to copy from.
```

--------------------------------

### Any Trait Implementation

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/ec/edwards25519/tai/struct.EdVrfEdwards25519TaiPublicKey.html

Gets the `TypeId` of `self`. This is part of the Any trait for dynamic type checking.

```rust
fn type_id(&self) -> TypeId
```

--------------------------------

### Ciphersuite PartialEq Implementation

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/struct.Ciphersuite.html

Enables equality comparison for Ciphersuite instances.

```APIDOC
## fn eq(&self, other: &Ciphersuite) -> bool

### Description
Tests for `self` and `other` values to be equal, and is used by `==`.

### Method
eq

### Parameters
- `self`: A reference to the first Ciphersuite instance.
- `other`: A reference to the second Ciphersuite instance.

### Returns
`true` if the instances are equal, `false` otherwise.
```

```APIDOC
## fn ne(&self, other: &Rhs) -> bool

### Description
Tests for `!=`.

### Method
ne

### Parameters
- `self`: A reference to the first Ciphersuite instance.
- `other`: A reference to the second Ciphersuite instance.

### Returns
`true` if the instances are not equal, `false` otherwise.
```

--------------------------------

### into_ok

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/error/type.VrfResult.html

Returns the contained `Ok` value, but never panics. This is an experimental API.

```APIDOC
## pub const fn into_ok(self) -> T

### Description
Returns the contained `Ok` value, but never panics.
Unlike `unwrap`, this method is known to never panic on the result types it is implemented for. Therefore, it can be used instead of `unwrap` as a maintainability safeguard that will fail to compile if the error type of the `Result` is later changed to an error that can actually occur.

### Examples
```rust
fn only_good_news() -> Result<String, !> {
    Ok("this is fine".into())
}

let s: String = only_good_news().into_ok();
println!("{s}");
```
```

--------------------------------

### Ciphersuite Hash Implementation

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/struct.Ciphersuite.html

Enables hashing of Ciphersuite instances.

```APIDOC
## fn hash<__H: Hasher>(&self, state: &mut __H)

### Description
Feeds this value into the given `Hasher`.

### Method
hash

### Parameters
- `self`: A reference to the Ciphersuite instance.
- `state`: A mutable reference to the Hasher.
```

```APIDOC
## fn hash_slice<H>(data: &[Self], state: &mut H)

### Description
Feeds a slice of this type into the given `Hasher`.

### Method
hash_slice

### Parameters
- `data`: A slice of Ciphersuite instances.
- `state`: A mutable reference to the Hasher.
```

--------------------------------

### Generate ECVRF Proof for P-256

Source: https://docs.rs/vrf-rfc9381/latest/src/vrf_rfc9381/ec/p256.rs.html

Generates an ECVRF proof using the P-256 curve. This involves nonce generation, challenge calculation, and final proof construction.

```rust
let mut k = self.generate_nonce(h.encode_to_curve_salt())?;
let k_nz = k.to_nonzero_scalar();
let k_h =
PublicKey::from_affine((h.point.to_projective() * k_nz.as_ref()).to_affine())?;
let c =
EcChallenge::generate(suite, &[&y.point, &h.point, &gamma, &k.public_key(), &k_h])?;

let c_x = c.to_nonzero_scalar() * x;
let Some(s_scalar) =
    p256::NonZeroScalar::new(k_nz.as_ref() + c_x.as_ref()).into_option()
else {
    unreachable!()
};
let s = SecretKey::from(s_scalar);

Ok(EcVrfProof { gamma, c, s })
```

--------------------------------

### Ciphersuite PartialOrd Implementation

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/struct.Ciphersuite.html

Provides methods for partial ordering comparison of Ciphersuite instances.

```APIDOC
## fn partial_cmp(&self, other: &Ciphersuite) -> Option<Ordering>

### Description
This method returns an ordering between `self` and `other` values if one exists.

### Method
partial_cmp

### Parameters
- `self`: A reference to the first Ciphersuite instance.
- `other`: A reference to the second Ciphersuite instance.

### Returns
An `Option<Ordering>` enum value indicating the relationship between the two instances, or `None` if they cannot be ordered.
```

```APIDOC
## fn lt(&self, other: &Rhs) -> bool

### Description
Tests less than (for `self` and `other`) and is used by the `<` operator.

### Method
lt

### Parameters
- `self`: A reference to the first Ciphersuite instance.
- `other`: A reference to the second Ciphersuite instance.

### Returns
`true` if `self` is less than `other`, `false` otherwise.
```

```APIDOC
## fn le(&self, other: &Rhs) -> bool

### Description
Tests less than or equal to (for `self` and `other`) and is used by the `<=` operator.

### Method
le

### Parameters
- `self`: A reference to the first Ciphersuite instance.
- `other`: A reference to the second Ciphersuite instance.

### Returns
`true` if `self` is less than or equal to `other`, `false` otherwise.
```

```APIDOC
## fn gt(&self, other: &Rhs) -> bool

### Description
Tests greater than (for `self` and `other`) and is used by the `>` operator.

### Method
gt

### Parameters
- `self`: A reference to the first Ciphersuite instance.
- `other`: A reference to the second Ciphersuite instance.

### Returns
`true` if `self` is greater than `other`, `false` otherwise.
```

```APIDOC
## fn ge(&self, other: &Rhs) -> bool

### Description
Tests greater than or equal to (for `self` and `other`) and is used by the `>=` operator.

### Method
ge

### Parameters
- `self`: A reference to the first Ciphersuite instance.
- `other`: A reference to the second Ciphersuite instance.

### Returns
`true` if `self` is greater than or equal to `other`, `false` otherwise.
```

--------------------------------

### EdVrfProof Equality Comparison

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/ec/edwards25519/struct.EdVrfProof.html

Implements PartialEq and Eq for EdVrfProof, enabling equality checks between instances.

```rust
fn eq(&self, other: &EdVrfProof) -> bool
```

```rust
fn ne(&self, other: &Rhs) -> bool
```

--------------------------------

### Handling File Metadata with and_then

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/error/type.VrfResult.html

Demonstrates using `and_then` with `Path::metadata` and `modified` to chain fallible file system operations. This pattern is useful for operations that depend on previous successful results.

```rust
use std::{io::ErrorKind, path::Path};

// Note: on Windows "/" maps to "C:\"
let root_modified_time = Path::new("/").metadata().and_then(|md| md.modified());
assert!(root_modified_time.is_ok());

let should_fail = Path::new("/bad/path").metadata().and_then(|md| md.modified());
assert!(should_fail.is_err());
assert_eq!(should_fail.unwrap_err().kind(), ErrorKind::NotFound);
```

--------------------------------

### Get Encode-to-Curve Salt

Source: https://docs.rs/vrf-rfc9381/latest/src/vrf_rfc9381/ec/edwards25519.rs.html

Retrieves the salt used for the encode-to-curve operation, derived from the compressed public key.

```rust
pub fn encode_to_curve_salt(&self) -> &[u8] {
            self.compressed.as_bytes().as_slice()
        }
    }
```

--------------------------------

### EdVrfProof Proof Encoding and Decoding

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/ec/edwards25519/struct.EdVrfProof.html

Provides methods for encoding an EdVrfProof to its byte representation (`pi_string`) and decoding from `pi_string` back into an EdVrfProof. These are part of the Proof trait implementation.

```rust
fn decode_pi(pi: &[u8]) -> VrfResult<Self>
```

```rust
fn encode_to_pi(&self) -> Vec<u8> ⓘ
```

--------------------------------

### Ciphersuite Ord Implementation

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/struct.Ciphersuite.html

Provides methods for ordering Ciphersuite instances.

```APIDOC
## fn cmp(&self, other: &Ciphersuite) -> Ordering

### Description
This method returns an `Ordering` between `self` and `other`.

### Method
cmp

### Parameters
- `self`: A reference to the first Ciphersuite instance.
- `other`: A reference to the second Ciphersuite instance.

### Returns
An `Ordering` enum value indicating the relationship between the two instances.
```

```APIDOC
## fn max(self, other: Self) -> Self

### Description
Compares and returns the maximum of two values.

### Method
max

### Parameters
- `self`: The first Ciphersuite instance.
- `other`: The second Ciphersuite instance.

### Returns
The maximum of the two Ciphersuite instances.
```

```APIDOC
## fn min(self, other: Self) -> Self

### Description
Compares and returns the minimum of two values.

### Method
min

### Parameters
- `self`: The first Ciphersuite instance.
- `other`: The second Ciphersuite instance.

### Returns
The minimum of the two Ciphersuite instances.
```

```APIDOC
## fn clamp(self, min: Self, max: Self) -> Self

### Description
Restrict a value to a certain interval.

### Method
clamp

### Parameters
- `self`: The Ciphersuite instance to clamp.
- `min`: The minimum allowed value.
- `max`: The maximum allowed value.

### Returns
The clamped Ciphersuite instance.
```

--------------------------------

### Get Verifier (Public Key) from Secret Key

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/ec/edwards25519/elligator2/struct.EdVrfEdwards25519Ell2SecretKey.html

Retrieves the corresponding public key (Verifier) for this secret key.

```rust
fn verifier(&self) -> Self::Verifier
```

--------------------------------

### Create Public Key from Bytes

Source: https://docs.rs/vrf-rfc9381/latest/src/vrf_rfc9381/ec/edwards25519.rs.html

Constructs an EdVrfEdwards25519PublicKey from a byte slice. Ensures the point is valid and not of small order.

```rust
pub fn from_bytes(bytes: &[u8]) -> VrfResult<Self> {
            let compressed = CompressedEdwardsY::from_slice(bytes)?;
            let point = compressed.decompress().ok_or(VrfError::InvalidEcPoint)?;
            if point.is_small_order() {
                return Err(VrfError::InvalidEcPoint);
            }

            Ok(Self { compressed, point })
        }
    }
```

--------------------------------

### Collecting Results into a Vector (Failure)

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/error/type.VrfResult.html

Demonstrates using `collect` on an iterator of Results, where an Err is encountered. This example checks for integer underflow.

```rust
let v = vec![1, 2, 0];
let res: Result<Vec<u32>, &'static str> = v.iter().map(|x: &u32| 
    x.checked_sub(1).ok_or("Underflow!")
).collect();
assert_eq!(res, Err("Underflow!"));
```

--------------------------------

### ECVRF Proof Verification Steps

Source: https://docs.rs/vrf-rfc9381/latest/src/vrf_rfc9381/ec/p256.rs.html

Implements the verification logic for an ECVRF proof, calculating intermediate values U and V and comparing the generated challenge c' with the provided challenge c. Returns an error if verification fails.

```rust
let u = s.public_key().to_projective() - (self.point.to_projective() * c_nz.as_ref());
            let u = PublicKey::from_affine(u.to_affine())?;
            // 9. V = s*H - c*Gamma
            let v = h.point.to_projective() * s_nz.as_ref() - gamma.to_projective() * c_nz.as_ref();
            let v = PublicKey::from_affine(v.to_affine())?;
            // 10. c' = ECVRF_challenge_generation(Y, H, Gamma, U, V) (see Section 5.4.3)
            let c_prime = EcChallenge::generate(suite, &[&self.point, &h.point, &gamma, &u, &v])?;

            // 11.  If c and c' are equal, output ("VALID", ECVRF_proof_to_hash(pi_string)); else output "INVALID"
            if c_prime != c {
                return Err(VrfError::ProofVerificationFailure);
            }

            Ok(EcVrfProof { gamma, c, s })
```

--------------------------------

### Ciphersuite Debug Implementation

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/struct.Ciphersuite.html

Allows for debugging Ciphersuite instances.

```APIDOC
## fn fmt(&self, f: &mut Formatter<'_>) -> Result

### Description
Formats the value using the given formatter.

### Method
fmt

### Parameters
- `self`: A reference to the Ciphersuite instance.
- `f`: A mutable reference to the formatter.
```

--------------------------------

### Providing a Default Value with unwrap_or

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/error/type.VrfResult.html

Use `unwrap_or` to get the `Ok` value or a specified default if the `Result` is `Err`. The default value is eagerly evaluated.

```rust
let default = 2;
let x: Result<u32, &str> = Ok(9);
assert_eq!(x.unwrap_or(default), 9);

let x: Result<u32, &str> = Err("error");
assert_eq!(x.unwrap_or(default), default);
```

--------------------------------

### Ciphersuite Method for EcVrfP256Sswu

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/ec/p256/sswu/struct.EcVrfP256Sswu.html

Returns the Ciphersuite used by the EcVrfP256Sswu implementation.

```rust
fn ciphersuite(&self) -> Ciphersuite

```

--------------------------------

### Unwrap Error Value (Basic Usage)

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/error/type.VrfResult.html

Use `unwrap_err()` to get the contained `Err` value. This method will panic if the `Result` is an `Ok`. It is useful when you expect an error and want to handle it.

```Rust
let x: Result<u32, &str> = Err("emergency failure");
assert_eq!(x.unwrap_err(), "emergency failure");
```

--------------------------------

### Eq and PartialEq for EcVrfP256SswuSecretKey

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/ec/p256/sswu/struct.EcVrfP256SswuSecretKey.html

Implementations for equality comparison, allowing secret keys to be compared for equality.

```APIDOC
### impl Eq for EcVrfP256SswuSecretKey

### impl PartialEq for EcVrfP256SswuSecretKey

#### fn eq(&self, other: &EcVrfP256SswuSecretKey) -> bool

Tests for `self` and `other` values to be equal, and is used by `==`.

#### fn ne(&self, other: &Rhs) -> bool

Tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
```

--------------------------------

### map_or

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/error/type.VrfResult.html

Applies a function to the Ok value or returns a default value if Err.

```APIDOC
## pub fn map_or<U, F>(self, default: U, f: F) -> U
where F: FnOnce(T) -> U,
Returns the provided default (if `Err`), or applies a function to the contained value (if `Ok`).

### Description
This method provides a way to handle both `Ok` and `Err` variants of a `VrfResult`. If the result is `Ok`, it applies a function `f` to the contained value. If it's `Err`, it returns a provided `default` value. Note that arguments are eagerly evaluated.

### Parameters
- `default`: The value to return if the `VrfResult` is `Err`.
- `f`: A closure that takes the `Ok` value `T` and returns a `U`.

### Returns
- `U`: The result of the function `f` if `Ok`, or the `default` value if `Err`.

### Examples
```rust
let x: Result<_, &str> = Ok("foo");
assert_eq!(x.map_or(42, |v| v.len()), 3);

let x: Result<&str, _> = Err("bar");
assert_eq!(x.map_or(42, |v| v.len()), 42);
```
```

--------------------------------

### Unwrap or Default Value

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/error/type.VrfResult.html

Use `unwrap_or_default()` to get the contained `Ok` value or a default value if the `Result` is an `Err`. This is useful for providing fallback values when an operation might fail.

```Rust
let good_year_from_input = "1909";
let bad_year_from_input = "190blarg";
let good_year = good_year_from_input.parse().unwrap_or_default();
let bad_year = bad_year_from_input.parse().unwrap_or_default();

assert_eq!(1909, good_year);
assert_eq!(0, bad_year);
```

--------------------------------

### Computing a Default Value with unwrap_or_else

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/error/type.VrfResult.html

Use `unwrap_or_else` to get the `Ok` value or compute a default value using a closure if the `Result` is `Err`. This is useful when the default value is expensive to compute.

```rust
fn count(x: &str) -> usize { x.len() }
```

--------------------------------

### VRF Provided Methods

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/trait.VRF.html

Details the default implementations for proof generation (`prove`) and verification (`verify`) within the VRF trait.

```rust
fn prove(&self, prover: &Self::Prover, alpha: &[u8]) -> VrfResult<Vec<u8>> { ... }
```

```rust
fn verify(
        &self,
        verifier: &Self::Verifier,
        alpha: &[u8],
        pi: &[u8],
    ) -> VrfResult<Output<Self::Hash>> { ... }
```

--------------------------------

### Proof to Hash Operation for EcVrfProof

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/ec/p256/struct.EcVrfProof.html

Performs the proof-to-hash operation on an EcVrfProof using a specified ciphersuite, returning the resulting hash output. This method is part of the Proof trait implementation for EcVrfProof.

```rust
fn proof_to_hash(&self, suite: Ciphersuite) -> VrfResult<Output<Sha256>>
```

--------------------------------

### Iterate Over Ok Value

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/error/type.VrfResult.html

Use `iter` to get an iterator that yields a reference to the contained value if the Result is `Ok`, otherwise yields nothing. This is useful for treating a Result as an optional collection.

```rust
let x: Result<u32, &str> = Ok(7);
assert_eq!(x.iter().next(), Some(&7));

let x: Result<u32, &str> = Err("nothing!");
assert_eq!(x.iter().next(), None);
```

--------------------------------

### ok

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/error/type.VrfResult.html

Converts a VrfResult into an Option, discarding the error value.

```APIDOC
## pub fn ok(self) -> Option<T>
Converts from `Result<T, E>` to `Option<T>`.

### Description
This method consumes the `VrfResult` and returns an `Option<T>`. If the `VrfResult` is `Ok(value)`, it returns `Some(value)`. If it is `Err`, it returns `None`.

### Returns
- `Option<T>`: `Some(T)` if the result was `Ok`, `None` if it was `Err`.

### Examples
```rust
let x: Result<u32, &str> = Ok(2);
assert_eq!(x.ok(), Some(2));

let x: Result<u32, &str> = Err("Nothing here");
assert_eq!(x.ok(), None);
```
```

--------------------------------

### Iterate Mutably Over Ok Value

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/error/type.VrfResult.html

Use `iter_mut` to get a mutable iterator that yields a mutable reference to the contained value if the Result is `Ok`, otherwise yields nothing. This allows in-place modification of the `Ok` value.

```rust
let mut x: Result<u32, &str> = Ok(7);
match x.iter_mut().next() {
    Some(v) => *v = 40,
    None => {},
}
assert_eq!(x, Ok(40));

let mut x: Result<u32, &str> = Err("nothing!");
assert_eq!(x.iter_mut().next(), None);
```

--------------------------------

### Into Ok Value (Never Panics)

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/error/type.VrfResult.html

Use `into_ok()` to safely extract the `Ok` value without panicking. This experimental API is guaranteed not to panic, serving as a compile-time safeguard against unexpected error types.

```Rust
fn only_good_news() -> Result<String, !> {
    Ok("this is fine".into())
}

let s: String = only_good_news().into_ok();
println!("{s}");
```

--------------------------------

### Expect Error Value with Custom Message

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/error/type.VrfResult.html

Use `expect_err()` to get the contained `Err` value. This method panics if the `Result` is an `Ok`, including a custom message provided as an argument. It's useful for asserting that an operation should fail.

```Rust
let x: Result<u32, &str> = Ok(10);
x.expect_err("Testing expect_err"); // panics with `Testing expect_err: 10`
```

--------------------------------

### Generic Type Conversion Implementations

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/ec/edwards25519/struct.EdVrfProof.html

Demonstrates various blanket implementations for generic types, including Any, Borrow, BorrowMut, From, Into, TryFrom, and TryInto. These are standard Rust trait implementations that apply to many types, including EdVrfProof.

```rust
fn type_id(&self) -> TypeId
```

```rust
fn borrow(&self) -> &T
```

```rust
fn borrow_mut(&mut self) -> &mut T
```

```rust
fn from(t: T) -> T
```

```rust
fn into(self) -> U
```

```rust
type Error = Infallible
```

```rust
fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>
```

```rust
type Error = <U as TryFrom<T>>::Error
```

```rust
fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>
```

--------------------------------

### Proof to Hash Operation

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/trait.Proof.html

Performs the proof-to-hash operation on the VRF Proof, returning the resulting hash output. Requires a Ciphersuite to be specified.

```rust
fn proof_to_hash(&self, suite: Ciphersuite) -> VrfResult<Output<H>>;
```

--------------------------------

### Hash Proof to Digest

Source: https://docs.rs/vrf-rfc9381/latest/src/vrf_rfc9381/ec/util.rs.html

Computes a hash of the proof data, including the ciphersuite and gamma string, using a specified digest algorithm. This is a common step in VRF verification.

```rust
pub(crate) fn proof_to_hash<H: digest::Digest>(
    suite: Ciphersuite,
    gamma_string: &[u8],
) -> digest::Output<H> {
    H::new()
        .chain_update([*suite, ECVRF_PROOF_DST_FRONT])
        .chain_update(gamma_string)
        .chain_update([ECVRF_PROOF_DST_BACK])
        .finalize()
}
```

--------------------------------

### Encode Proof to Pi String

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/trait.Proof.html

Encodes the current proof instance into a `pi_string` (byte vector).

```rust
fn encode_to_pi(&self) -> Vec<u8> ⓘ;
```

--------------------------------

### EdVrfEdwards25519Ell2PublicKey Verifier Methods

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/ec/edwards25519/elligator2/struct.EdVrfEdwards25519Ell2PublicKey.html

This section details the methods available for verifying VRF proofs using the EdVrfEdwards25519Ell2PublicKey as a Verifier.

```APIDOC
## Trait Implementations

### impl Verifier<Sha512> for EdVrfEdwards25519Ell2PublicKey

#### type Proof = EdVrfProof

The Proof that this Verifier can verify.

#### fn from_slice(bytes: &[u8]) -> VrfResult<Self>

Creates a new public key from a byte slice.

#### fn verify(&self, alpha: &[u8], proof: Self::Proof) -> VrfResult<Output<Sha512>>

Verifies a (alpha, proof) combination. Outputs the VRF_proof_to_hash if successful.
```

--------------------------------

### EdVrfProof Debug Implementation

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/ec/edwards25519/struct.EdVrfProof.html

Provides a Debug implementation for EdVrfProof, allowing it to be formatted for debugging purposes.

```rust
fn fmt(&self, f: &mut Formatter<'_>) -> Result
```

--------------------------------

### VRF Required Methods

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/trait.VRF.html

Specifies the essential methods that must be implemented for any VRF type, including retrieving the ciphersuite.

```rust
fn ciphersuite(&self) -> Ciphersuite;
```

--------------------------------

### Prove Method for EcVrfP256Sswu

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/ec/p256/sswu/struct.EcVrfP256Sswu.html

Generates a VRF proof for a given prover and input alpha. This method outputs the proof as a byte vector.

```rust
fn prove(&self, prover: &Self::Prover, alpha: &[u8]) -> VrfResult<Vec<u8>>

```

--------------------------------

### Convert &Result to Result<&T, &E>

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/error/type.VrfResult.html

Use `as_ref()` to convert a reference to a `Result` (`&Result<T, E>`) into a `Result` containing references (`Result<&T, &E>`). This allows inspecting the `Result`'s contents without taking ownership.

```rust
let x: Result<u32, &str> = Ok(2);
assert_eq!(x.as_ref(), Ok(&2));

let x: Result<u32, &str> = Err("Error");
assert_eq!(x.as_ref(), Err(&"Error"));
```

--------------------------------

### Generate Challenge Bytes

Source: https://docs.rs/vrf-rfc9381/latest/src/vrf_rfc9381/ec/util.rs.html

Generates a fixed-length challenge byte array from an iterator of points. It incorporates the ciphersuite and specific domain separators. Asserts that exactly 5 points are processed.

```rust
pub(crate) fn challenge_bytes<'a, const CHALLENGE_LEN: usize, H: digest::Digest>(
    suite: Ciphersuite,
    points: impl Iterator<Item = &'a [u8]>, // Assuming points are byte slices
) -> zeroize::Zeroizing<[u8; CHALLENGE_LEN]> {
    let mut hasher = H::new();
    hasher.update([*suite, ECVRF_CHAL_GEN_DST_FRONT]);
    let mut point_count = 0u8;
    for point in points {
        hasher.update(point);
        point_count += 1;
    }
    debug_assert_eq!(point_count, 5, "Point count MUST be 5");
    hasher.update([ECVRF_CHAL_GEN_DST_BACK]);
    let c_string = hasher.finalize();

    zeroize::Zeroizing::new(c_string[..CHALLENGE_LEN].try_into().unwrap())
}
```

--------------------------------

### EdVrfProof Pinned Drop Implementation (Nightly/Experimental)

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/ec/edwards25519/struct.EdVrfProof.html

An experimental, nightly-only API for executing the destructor of EdVrfProof when the value is pinned. This differs from the standard `Drop::drop` by requiring a pinned `self`.

```rust
fn pin_drop(self: Pin<&mut Self>)
```

--------------------------------

### Clone Implementation

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/error/type.VrfResult.html

Provides methods for cloning a Result, allowing for duplication of the Ok or Err values if they themselves are Clone.

```APIDOC
## impl<T, E> Clone for Result<T, E>

### fn clone(&self) -> Result<T, E>

Returns a duplicate of the value.

### fn clone_from(&mut self, source: &Result<T, E>)

Performs copy-assignment from `source`.
```

--------------------------------

### Create Secret Key from Slice

Source: https://docs.rs/vrf-rfc9381/latest/src/vrf_rfc9381/ec/p256.rs.html

Creates a P-256 secret key from a byte slice. Pads the slice with zeros if it's shorter than the expected key length.

```rust
pub(super) fn sk_from_slice(slice: &[u8]) -> VrfResult<SecretKey> {
        assert!(slice.len() <= Q_LEN);
        let offset = Q_LEN.saturating_sub(slice.len());
        let mut c_scalar_bytes: p256::FieldBytes = Default::default();
        c_scalar_bytes[offset..].copy_from_slice(slice);
        Ok(SecretKey::from_bytes(&c_scalar_bytes)?)
    }
```

--------------------------------

### P256 SSWU VRF Prover Implementation

Source: https://docs.rs/vrf-rfc9381/latest/src/vrf_rfc9381/ec/p256.rs.html

Implements the Prover trait for the P256 SSWU ciphersuite. This enables VRF proof generation using a secret key. It includes methods for reconstructing the secret key from a byte slice and for generating proofs for given messages.

```rust
impl crate::Prover<sha2::Sha256> for EcVrfP256SswuSecretKey {
    type Proof = EcVrfProof;

    type Verifier = EcVrfP256SswuPublicKey;

    fn from_slice(bytes: &[u8]) -> VrfResult<Self>
    where
        Self: Sized,
    {
        Ok(Self(EcVrfP256SecretKey::from_sk(bytes.try_into()?)?))
    }

    #[cfg(feature = "hazmat")]
    fn x_equals(&self, value: &[u8]) -> bool {
        self.0.x_equals(value)
    }

    fn verifier(&self) -> Self::Verifier {
        EcVrfP256SswuPublicKey(self.0.public_key())
    }

    fn prove(&self, alpha: &[u8]) -> VrfResult<Self::Proof> {
        self.0.prove(Ciphersuite::ECVRF_P256_SHA256_SSWU, alpha)
    }
}
```

--------------------------------

### Generate VRF Proof

Source: https://docs.rs/vrf-rfc9381/latest/src/vrf_rfc9381/ec/p256.rs.html

Generates a VRF proof for a given ciphersuite and alpha value using the P-256 curve. This involves deriving the secret scalar, computing the public key, and then calculating the gamma point.

```rust
pub(super) fn prove(&self, suite: Ciphersuite, alpha: &[u8]) -> VrfResult<EcVrfProof> {
            // 1. Use SK to derive the VRF secret scalar x and the VRF public key Y = x*B
            let y = self.public_key();
            // 2. H = ECVRF_encode_to_curve(encode_to_curve_salt, alpha_string) (see Section 5.4.1)
            let h = y.encode_to_curve(suite, alpha)?;

            let x = self.0.to_nonzero_scalar();
            // 3. Gamma = x*H
            let gamma = h.point.to_projective() * x.as_ref();
            let gamma = PublicKey::from_affine(gamma.to_affine())?;
            
```

--------------------------------

### Verify ECVRF Proof for P-256

Source: https://docs.rs/vrf-rfc9381/latest/src/vrf_rfc9381/ec/p256.rs.html

Verifies an ECVRF proof against a P-256 public key and associated data. It decodes the proof and performs cryptographic checks.

```rust
let EcVrfProof { gamma, c, s } = proof;
let h = self.encode_to_curve(suite, alpha)?;

let c_nz = c.to_nonzero_scalar();
let s_nz = s.to_nonzero_scalar();

// 8. U = s*B - c*Y
```

--------------------------------

### Convert Result to Option with Ok value

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/error/type.VrfResult.html

The `ok()` method converts a `Result<T, E>` into an `Option<T>`. If the `Result` is `Ok(v)`, it returns `Some(v)`. If it's `Err(_)`, it returns `None`. This consumes the `Result`.

```rust
let x: Result<u32, &str> = Ok(2);
assert_eq!(x.ok(), Some(2));

let x: Result<u32, &str> = Err("Nothing here");
assert_eq!(x.ok(), None);
```

--------------------------------

### TryInto Conversion Implementation

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/ec/edwards25519/tai/struct.EdVrfEdwards25519TaiSecretKey.html

Performs the conversion. This is a blanket implementation for the TryInto trait.

```rust
fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>
```

--------------------------------

### unwrap_or_else<F>

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/error/type.VrfResult.html

Returns the contained `Ok` value or computes it from a closure.

```APIDOC
## pub fn unwrap_or_else<F>(self, op: F) -> T
where F: FnOnce(E) -> T

### Description
Returns the contained `Ok` value or computes it from a closure.

### Method
`unwrap_or_else`

### Parameters
#### Request Body
- **op** (FnOnce(E) -> T) - A closure that takes the error value and returns a value of type `T`.

### Request Example
```rust
fn count(x: &str) -> usize { x.len() }

let x: Result<&str, &str> = Ok("hello");
assert_eq!(x.unwrap_or_else(count), 5);

let x: Result<&str, &str> = Err("error");
assert_eq!(x.unwrap_or_else(count), 5);
```

### Response
#### Success Response (T)
- **T**: The contained `Ok` value or the value computed by the closure.

#### Response Example
```rust
// Example for Ok("hello").unwrap_or_else(count) -> 5
// Example for Err("error").unwrap_or_else(count) -> 5
```
```

--------------------------------

### Try for Result<T, E>

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/error/type.VrfResult.html

Experimental nightly-only API for the `?` operator, defining output, residual types, and methods for handling results.

```APIDOC
## type Output = T

### Description
The type of the value produced by `?` when _not_ short-circuiting.

### Type
`Output`
```

```APIDOC
## type Residual = Result<Infallible, E>

### Description
The type of the value passed to `FromResidual::from_residual` as part of `?` when short-circuiting.

### Type
`Residual`
```

```APIDOC
## fn from_output(output: <Result<T, E> as Try>::Output) -> Result<T, E>

### Description
Constructs the type from its `Output` type.

### Method
`from_output`
```

```APIDOC
## fn branch( self, ) -> ControlFlow<<Result<T, E> as Try>::Residual, <Result<T, E> as Try>::Output>

### Description
Used in `?` to decide whether the operator should produce a value (because this returned `ControlFlow::Continue`) or propagate a value back to the caller (because this returned `ControlFlow::Break`).

### Method
`branch`
```

--------------------------------

### Ciphersuite Blanket Implementations

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/struct.Ciphersuite.html

Details the blanket trait implementations applicable to Ciphersuite.

```APIDOC
## Blanket Implementations

### impl<T> Any for T
where T: 'static + ?Sized,
#### fn type_id(&self) -> TypeId
Gets the `TypeId` of `self`. Read more

### impl<T> Borrow<T> for T
where T: ?Sized,
#### fn borrow(&self) -> &T
Immutably borrows from an owned value. Read more

### impl<T> BorrowMut<T> for T
where T: ?Sized,
#### fn borrow_mut(&mut self) -> &mut T
Mutably borrows from an owned value. Read more

### impl<T> CloneToUninit for T
where T: Clone,
#### unsafe fn clone_to_uninit(&self, dest: *mut u8)
Performs copy-assignment from `self` to `dest`.

### impl<T> From<T> for T
#### fn from(t: T) -> T
Returns the argument unchanged.

### impl<T, U> Into<U> for T
where U: From<T>,
#### fn into(self) -> U
Calls `U::from(self)`.

### impl<P, T> Receiver for P
where P: Deref<Target = T> + ?Sized, T: ?Sized,
#### type Target = T
The target type on which the method may be called.

### impl<T> Same for T
#### type Output = T
Should always be `Self`

### impl<T> ToOwned for T
where T: Clone,
#### type Owned = T
The resulting type after obtaining ownership.
#### fn to_owned(&self) -> T
Creates owned data from borrowed data, usually by cloning. Read more
#### fn clone_into(&self, target: &mut T)
Uses borrowed data to replace owned data, usually by cloning. Read more

### impl<T> ToString for T
where T: Display + ?Sized,
#### fn to_string(&self) -> String
Converts the given value to a `String`. Read more

### impl<T, U> TryFrom<U> for T
where U: Into<T>,
#### type Error = Infallible
The type returned in the event of a conversion error.
#### fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>
Performs the conversion.

### impl<T, U> TryInto<U> for T
where U: TryFrom<T>,
#### type Error = <U as TryFrom<T>>::Error
The type returned in the event of a conversion error.
#### fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>
Performs the conversion.
```

--------------------------------

### Prover::prove Method

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/trait.Prover.html

Generates a VRF Proof for a given input `alpha`.

```rust
fn prove(&self, alpha: &[u8]) -> VrfResult<Self::Proof>;
```

--------------------------------

### TryFrom Conversion Implementation

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/ec/edwards25519/tai/struct.EdVrfEdwards25519TaiSecretKey.html

Performs the conversion. This is a blanket implementation for the TryFrom trait.

```rust
fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>
```

--------------------------------

### EcVrfP256TaiSecretKey - Trait Implementations

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/ec/p256/tai/struct.EcVrfP256TaiSecretKey.html

This section details the available trait implementations for EcVrfP256TaiSecretKey, including Prover, Eq, PartialEq, and Drop.

```APIDOC
## Trait Implementations

### impl Drop for EcVrfP256TaiSecretKey

#### fn drop(&mut self)

Executes the destructor for this type. Read more

### impl Eq for EcVrfP256TaiSecretKey

### impl PartialEq for EcVrfP256TaiSecretKey

#### fn eq(&self, other: &EcVrfP256TaiSecretKey) -> bool

Tests for `self` and `other` values to be equal, and is used by `==`.

#### fn ne(&self, other: &Rhs) -> bool

Tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.

### impl Prover<Sha256> for EcVrfP256TaiSecretKey

#### type Proof = EcVrfProof

The Proof emitted by this Prover

#### type Verifier = EcVrfP256TaiPublicKey

The public counterpart (Verifier) of this Prover

#### fn from_slice(bytes: &[u8]) -> VrfResult<Self>

Deserialize a Prover from its byte representation

#### fn x_equals(&self, value: &[u8]) -> bool

Available on **crate feature`hazmat`** only.
Hazmat internal allowing to check if the scalar x equals a value. Do not use!

#### fn verifier(&self) -> Self::Verifier

Get the public counterpart of this Prover

#### fn prove(&self, alpha: &[u8]) -> VrfResult<Self::Proof>

Proves `alpha` as a VRF Proof
```

--------------------------------

### Generic Trait Implementations

Source: https://docs.rs/vrf-rfc9381/latest/vrf_rfc9381/ec/p256/sswu/struct.EcVrfP256SswuPublicKey.html

Demonstrates various auto-derived and blanket trait implementations for EcVrfP256SswuPublicKey, including Send, Sync, Freeze, and others.

```rust
fn type_id(&self) -> TypeId
```

```rust
fn borrow(&self) -> &T
```

```rust
fn borrow_mut(&mut self) -> &mut T
```

```rust
fn from(t: T) -> T
```

```rust
fn into(self) -> U
```

```rust
type Output = T
```

```rust
type Error = Infallible
```

```rust
fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>
```

```rust
type Error = <U as TryFrom<T>>::Error
```

```rust
fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>
```
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