Struct akd::ecvrf::VRFPublicKey
source · pub struct VRFPublicKey(/* private fields */);
Expand description
An ECVRF public key
Implementations§
source§impl VRFPublicKey
impl VRFPublicKey
sourcepub fn verify(&self, proof: &Proof, alpha: &[u8]) -> Result<(), VrfError>
pub fn verify(&self, proof: &Proof, alpha: &[u8]) -> Result<(), VrfError>
Given a Proof
and an input, returns whether or not the proof is valid for the input
and public key.
Note that public key validation occurs in the TryFrom implementation for VRFPublicKey, as well as the From implementation for VRFPrivateKey (implicitly in the ed25519_dalek library). Therefore, we do not perform public key validation in the verification function itself.
Methods from Deref<Target = VerifyingKey>§
pub fn with_context<'k, 'v>(
&'k self,
context_value: &'v [u8]
) -> Result<Context<'k, 'v, VerifyingKey>, Error>
pub fn with_context<'k, 'v>( &'k self, context_value: &'v [u8] ) -> Result<Context<'k, 'v, VerifyingKey>, Error>
Create a verifying context that can be used for Ed25519ph with
[DigestVerifier
].
pub fn is_weak(&self) -> bool
pub fn is_weak(&self) -> bool
Returns whether this is a weak public key, i.e., if this public key has low order.
A weak public key can be used to generate a signature that’s valid for almost every
message. [Self::verify_strict
] denies weak keys, but if you want to check for this
property before verification, then use this method.
pub fn verify_prehashed<MsgDigest>(
&self,
prehashed_message: MsgDigest,
context: Option<&[u8]>,
signature: &Signature
) -> Result<(), Error>where
MsgDigest: Digest<OutputSize = UInt<UInt<UInt<UInt<UInt<UInt<UInt<UTerm, B1>, B0>, B0>, B0>, B0>, B0>, B0>>,
pub fn verify_prehashed<MsgDigest>( &self, prehashed_message: MsgDigest, context: Option<&[u8]>, signature: &Signature ) -> Result<(), Error>where MsgDigest: Digest<OutputSize = UInt<UInt<UInt<UInt<UInt<UInt<UInt<UTerm, B1>, B0>, B0>, B0>, B0>, B0>, B0>>,
Verify a signature
on a prehashed_message
using the Ed25519ph algorithm.
Inputs
prehashed_message
is an instantiated hash digest with 512-bits of output which has had the message to be signed previously fed into its state.context
is an optional context string, up to 255 bytes inclusive, which may be used to provide additional domain separation. If not set, this will default to an empty string.signature
is a purported Ed25519ph signature on theprehashed_message
.
Returns
Returns true
if the signature
was a valid signature created by this
[SigningKey
] on the prehashed_message
.
Note
The RFC only permits SHA-512 to be used for prehashing, i.e., MsgDigest = Sha512
. This
function technically works, and is probably safe to use, with any secure hash function with
512-bit digests, but anything outside of SHA-512 is NOT specification-compliant. We expose
[crate::Sha512
] for user convenience.
pub fn verify_strict(
&self,
message: &[u8],
signature: &Signature
) -> Result<(), Error>
pub fn verify_strict( &self, message: &[u8], signature: &Signature ) -> Result<(), Error>
Strictly verify a signature on a message with this keypair’s public key.
On The (Multiple) Sources of Malleability in Ed25519 Signatures
This version of verification is technically non-RFC8032 compliant. The following explains why.
- Scalar Malleability
The authors of the RFC explicitly stated that verification of an ed25519
signature must fail if the scalar s
is not properly reduced mod $\ell$:
To verify a signature on a message M using public key A, with F being 0 for Ed25519ctx, 1 for Ed25519ph, and if Ed25519ctx or Ed25519ph is being used, C being the context, first split the signature into two 32-octet halves. Decode the first half as a point R, and the second half as an integer S, in the range 0 <= s < L. Decode the public key A as point A’. If any of the decodings fail (including S being out of range), the signature is invalid.)
All verify_*()
functions within ed25519-dalek perform this check.
- Point malleability
The authors of the RFC added in a malleability check to step #3 in
§5.1.7, for small torsion components in the R
value of the signature,
which is not strictly required, as they state:
Check the group equation [8][S]B = [8]R + [8][k]A’. It’s sufficient, but not required, to instead check [S]B = R + [k]A’.
History of Malleability Checks
As originally defined (cf. the “Malleability” section in the README of this repo), ed25519 signatures didn’t consider any form of malleability to be an issue. Later the scalar malleability was considered important. Still later, particularly with interests in cryptocurrency design and in unique identities (e.g. for Signal users, Tor onion services, etc.), the group element malleability became a concern.
However, libraries had already been created to conform to the original definition. One well-used library in particular even implemented the group element malleability check, but only for batch verification! Which meant that even using the same library, a single signature could verify fine individually, but suddenly, when verifying it with a bunch of other signatures, the whole batch would fail!
“Strict” Verification
This method performs both of the above signature malleability checks.
It must be done as a separate method because one doesn’t simply get to change the definition of a cryptographic primitive ten years after-the-fact with zero consideration for backwards compatibility in hardware and protocols which have it already have the older definition baked in.
Return
Returns Ok(())
if the signature is valid, and Err
otherwise.
pub fn verify_prehashed_strict<MsgDigest>(
&self,
prehashed_message: MsgDigest,
context: Option<&[u8]>,
signature: &Signature
) -> Result<(), Error>where
MsgDigest: Digest<OutputSize = UInt<UInt<UInt<UInt<UInt<UInt<UInt<UTerm, B1>, B0>, B0>, B0>, B0>, B0>, B0>>,
pub fn verify_prehashed_strict<MsgDigest>( &self, prehashed_message: MsgDigest, context: Option<&[u8]>, signature: &Signature ) -> Result<(), Error>where MsgDigest: Digest<OutputSize = UInt<UInt<UInt<UInt<UInt<UInt<UInt<UTerm, B1>, B0>, B0>, B0>, B0>, B0>, B0>>,
Verify a signature
on a prehashed_message
using the Ed25519ph algorithm,
using strict signture checking as defined by [Self::verify_strict
].
Inputs
prehashed_message
is an instantiated hash digest with 512-bits of output which has had the message to be signed previously fed into its state.context
is an optional context string, up to 255 bytes inclusive, which may be used to provide additional domain separation. If not set, this will default to an empty string.signature
is a purported Ed25519ph signature on theprehashed_message
.
Returns
Returns true
if the signature
was a valid signature created by this
[SigningKey
] on the prehashed_message
.
Note
The RFC only permits SHA-512 to be used for prehashing, i.e., MsgDigest = Sha512
. This
function technically works, and is probably safe to use, with any secure hash function with
512-bit digests, but anything outside of SHA-512 is NOT specification-compliant. We expose
[crate::Sha512
] for user convenience.
pub fn to_montgomery(&self) -> MontgomeryPoint
pub fn to_montgomery(&self) -> MontgomeryPoint
Convert this verifying key into Montgomery form.
This can be used for performing X25519 Diffie-Hellman using Ed25519 keys. The output of
this function is a valid X25519 public key whose secret key is sk.to_scalar_bytes()
,
where sk
is a valid signing key for this VerifyingKey
.
Note
We do NOT recommend this usage of a signing/verifying key. Signing keys are usually long-term keys, while keys used for key exchange should rather be ephemeral. If you can help it, use a separate key for encryption.
For more information on the security of systems which use the same keys for both signing and Diffie-Hellman, see the paper On using the same key pair for Ed25519 and an X25519 based KEM.
Trait Implementations§
source§impl Clone for VRFPublicKey
impl Clone for VRFPublicKey
source§fn clone(&self) -> VRFPublicKey
fn clone(&self) -> VRFPublicKey
1.0.0 · source§fn clone_from(&mut self, source: &Self)
fn clone_from(&mut self, source: &Self)
source
. Read moresource§impl Debug for VRFPublicKey
impl Debug for VRFPublicKey
source§impl Deref for VRFPublicKey
impl Deref for VRFPublicKey
source§impl<'a> From<&'a VRFPrivateKey> for VRFPublicKey
impl<'a> From<&'a VRFPrivateKey> for VRFPublicKey
source§fn from(private_key: &'a VRFPrivateKey) -> VRFPublicKey
fn from(private_key: &'a VRFPrivateKey) -> VRFPublicKey
source§impl PartialEq for VRFPublicKey
impl PartialEq for VRFPublicKey
source§fn eq(&self, other: &VRFPublicKey) -> bool
fn eq(&self, other: &VRFPublicKey) -> bool
self
and other
values to be equal, and is used
by ==
.