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use p256::ecdsa::{SigningKey, signature::SignerMut};
use passkey_types::{
Bytes,
ctap2::{
AuthenticatorData, Ctap2Error, Flags, StatusCode,
get_assertion::{Request, Response},
},
webauthn::PublicKeyCredentialUserEntity,
};
use crate::{
Authenticator, CredentialStore, UserValidationMethod,
passkey::{AsCredentialDescriptor, PasskeyAccessor},
private_key_from_cose_key,
user_validation::UiHint,
};
impl<S, U> Authenticator<S, U>
where
S: CredentialStore + Sync,
U: UserValidationMethod<PasskeyItem = <S as CredentialStore>::PasskeyItem> + Sync,
{
/// This method is used by a host to request cryptographic proof of user authentication as well
/// as user consent to a given transaction, using a previously generated credential that is
/// bound to the authenticator and relying party identifier.
pub async fn get_assertion(&mut self, input: Request) -> Result<Response, StatusCode> {
// 1. Locate all credentials that are eligible for retrieval under the specified criteria:
// 1. If an allowList is present and is non-empty, locate all denoted credentials
// present on this authenticator and bound to the specified rpId.
// 2. If an allowList is not present, locate all credentials that are present on this
// authenticator and bound to the specified rpId.
// 3. Let numberOfCredentials be the number of credentials found.
// --> Seeing as we handle 1 credential per account for an RP, returning the number
// of credentials leaks the number of accounts that is stored. This is not ideal,
// therefore we will never populate this field.
let maybe_credential = self
.store()
.find_credentials(
input
.allow_list
.as_deref()
.filter(|inner| !inner.is_empty()),
&input.rp_id,
// User handle is not available in assertion calls
None,
)
.await
.and_then(|c| c.into_iter().next().ok_or(Ctap2Error::NoCredentials.into()));
// 2. If pinAuth parameter is present and pinProtocol is 1, verify it by matching it against
// first 16 bytes of HMAC-SHA-256 of clientDataHash parameter using
// pinToken: HMAC-SHA-256(pinToken, clientDataHash).
// 1. If the verification succeeds, set the "uv" bit to 1 in the response.
// 2. If the verification fails, return CTAP2_ERR_PIN_AUTH_INVALID error.
// 3. If pinAuth parameter is present and the pinProtocol is not supported,
// return CTAP2_ERR_PIN_AUTH_INVALID.
// 4. If pinAuth parameter is not present and clientPin has been set on the authenticator,
// set the "uv" bit to 0 in the response.
if input.pin_auth.is_some() {
return Err(Ctap2Error::PinAuthInvalid.into());
}
// 5. If the options parameter is present, process all the options.
// 1. If the option is known but not supported, terminate this procedure and
// return CTAP2_ERR_UNSUPPORTED_OPTION.
// 2. If the option is known but not valid for this command, terminate this procedure
// and return CTAP2_ERR_INVALID_OPTION.
// 3. Ignore any options that are not understood.
// Note that because this specification defines normative behaviors for them, all
// authenticators MUST understand the "rk", "up", and "uv" options.
// 6. TODO, if the extensions parameter is present, process any extensions that this
// authenticator supports. Authenticator extension outputs generated by the authenticator
// extension processing are returned in the authenticator data.
// 7. Collect user consent if required. This step MUST happen before the following steps due
// to privacy reasons (i.e., authenticator cannot disclose existence of a credential
// until the user interacted with the device):
let hint = match &maybe_credential {
Ok(credential) => UiHint::RequestExistingCredential(credential),
Err(_) => UiHint::InformNoCredentialsFound,
};
let flags = self.check_user(hint, &input.options).await?;
// 8. If no credentials were located in step 1, return CTAP2_ERR_NO_CREDENTIALS.
let mut credential = maybe_credential?;
// 9. If more than one credential was located in step 1 and allowList is present and not
// empty, select any applicable credential and proceed to step 12. Otherwise, order the
// credentials by the time when they were created in reverse order. The first credential
// is the most recent credential that was created.
// NB: This should be done within the `CredentialStore::find_any` implementation. Essentially
// if multiple credentials are found, use the most recently created one.
// 10. If authenticator does not have a display:
// 1. Remember the authenticatorGetAssertion parameters.
// 2. Create a credential counter(credentialCounter) and set it 1. This counter
// signifies how many credentials are sent to the platform by the authenticator.
// 3. Start a timer. This is used during authenticatorGetNextAssertion command.
// This step is optional if transport is done over NFC.
// 4. Update the response to include the first credential’s publicKeyCredentialUserEntity
// information and numberOfCredentials. User identifiable information (name,
// DisplayName, icon) inside publicKeyCredentialUserEntity MUST not be returned if
// user verification is not done by the authenticator.
// 11. If authenticator has a display:
// 1. Display all these credentials to the user, using their friendly name along with
// other stored account information.
// 2. Also, display the rpId of the requester (specified in the request) and ask the
// user to select a credential.
// 3. If the user declines to select a credential or takes too long (as determined by
// the authenticator), terminate this procedure and return the
// CTAP2_ERR_OPERATION_DENIED error.
// [WebAuthn-9]. Increment the credential associated signature counter or the global signature
// counter value, depending on which approach is implemented by the authenticator,
// by some positive value. If the authenticator does not implement a signature
// counter, let the signature counter value remain constant at zero.
if let Some(counter) = credential.counter() {
credential.set_counter(counter + 1);
self.store_mut().update_credential(&credential).await?;
}
let extensions =
self.get_extensions(&credential, input.extensions, flags.contains(Flags::UV))?;
// 12. Sign the clientDataHash along with authData with the selected credential.
// Let signature be the assertion signature of the concatenation `authenticatorData` ||
// `client_data_hash` using the privateKey of selectedCredential. A simple, undelimited
// concatenation is safe to use here because the authenticator data describes its own
// length. The hash of the serialized client data (which potentially has a variable
// length) is always the last element.
let auth_data = AuthenticatorData::new(&input.rp_id, credential.counter())
.set_flags(flags)
.set_assertion_extensions(extensions.signed)?;
let mut signature_target = auth_data.to_vec();
signature_target.extend(input.client_data_hash);
let secret_key = private_key_from_cose_key(&credential.key())?;
let mut private_key = SigningKey::from(secret_key);
let signature: p256::ecdsa::Signature = private_key.sign(&signature_target);
let signature_bytes = signature.to_der().to_bytes().to_vec().into();
let user_handle = credential.user_handle().map(Bytes::from);
Ok(Response {
credential: Some(credential.as_credential_descriptor(None)),
auth_data,
signature: signature_bytes,
user: user_handle.map(|id| PublicKeyCredentialUserEntity {
id,
// TODO: make a Authenticator version of this struct similar to make_credential::PublicKeyCredentialRpEntity
// since these fields are optional at the authenticator boundary, but required at the client boundary.
display_name: "".into(),
name: "".into(),
}),
number_of_credentials: None,
user_selected: None,
large_blob_key: None,
unsigned_extension_outputs: extensions.unsigned,
})
}
}
#[cfg(test)]
mod tests;