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ctap2: Implement permissions
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@robin-nitrokey
robin-nitrokey committed Mar 1, 2024
1 parent bf61fcd commit 87e3aef
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1 change: 1 addition & 0 deletions CHANGELOG.md
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Expand Up @@ -21,6 +21,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
- PIN protocol changes:
- Extract PIN protocol implementation into separate module ([#62][])
- Implement PIN protocol 2 ([#63][])
- Implement PIN token permissions ([#63][])

[#26]: https://github.com/solokeys/fido-authenticator/issues/26
[#28]: https://github.com/solokeys/fido-authenticator/issues/28
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2 changes: 1 addition & 1 deletion Cargo.toml
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Expand Up @@ -57,7 +57,7 @@ usbd-ctaphid = "0.1.0"
features = ["dispatch"]

[patch.crates-io]
ctap-types = { git = "https://github.com/trussed-dev/ctap-types.git", rev = "3735eb5a8e2b30b98afd35b64b4f470e690dcd19" }
ctap-types = { git = "https://github.com/trussed-dev/ctap-types.git", rev = "4846817d9cd44604121680a19d46f3264973a3ce" }
ctaphid-dispatch = { git = "https://github.com/trussed-dev/ctaphid-dispatch.git", rev = "57cb3317878a8593847595319aa03ef17c29ec5b" }
apdu-dispatch = { git = "https://github.com/trussed-dev/apdu-dispatch.git", rev = "915fc237103fcecc29d0f0b73391f19abf6576de" }
littlefs2 = { git = "https://github.com/trussed-dev/littlefs2.git", rev = "ebd27e49ca321089d01d8c9b169c4aeb58ceeeca" }
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225 changes: 153 additions & 72 deletions src/ctap2.rs
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Original file line number Diff line number Diff line change
@@ -1,7 +1,7 @@
//! The `ctap_types::ctap2::Authenticator` implementation.

use ctap_types::{
ctap2::{self, Authenticator, VendorOperation},
ctap2::{self, client_pin::Permissions, Authenticator, VendorOperation},
heapless::{String, Vec},
heapless_bytes::Bytes,
sizes, Error,
Expand Down Expand Up @@ -86,6 +86,7 @@ impl<UP: UserPresence, T: TrussedRequirements> Authenticator for crate::Authenti
},
credential_mgmt_preview: Some(true),
large_blobs: Some(self.config.supports_large_blobs()),
pin_uv_auth_token: Some(true),
..Default::default()
};
// options.rk = true;
Expand Down Expand Up @@ -174,6 +175,8 @@ impl<UP: UserPresence, T: TrussedRequirements> Authenticator for crate::Authenti
parameters.pin_auth.map(AsRef::as_ref),
parameters.pin_protocol,
parameters.client_data_hash.as_ref(),
Permissions::MAKE_CREDENTIAL,
&parameters.rp.id,
)?;

// 5. "persist credProtect value for this credential"
Expand Down Expand Up @@ -644,28 +647,19 @@ impl<UP: UserPresence, T: TrussedRequirements> Authenticator for crate::Authenti
// info_now!("{:?}", parameters);

let pin_protocol = self.parse_pin_protocol(parameters.pin_protocol)?;
let mut response = ctap2::client_pin::Response::default();

Ok(match parameters.sub_command {
match parameters.sub_command {
Subcommand::GetRetries => {
debug_now!("CTAP2.Pin.GetRetries");

ctap2::client_pin::Response {
key_agreement: None,
pin_token: None,
retries: Some(self.state.persistent.retries()),
}
response.retries = Some(self.state.persistent.retries());
}

Subcommand::GetKeyAgreement => {
debug_now!("CTAP2.Pin.GetKeyAgreement");

let key_agreement = self.pin_protocol(pin_protocol).key_agreement_key();

ctap2::client_pin::Response {
key_agreement: Some(key_agreement),
pin_token: None,
retries: None,
}
response.key_agreement = Some(self.pin_protocol(pin_protocol).key_agreement_key());
}

Subcommand::SetPin => {
Expand Down Expand Up @@ -716,12 +710,6 @@ impl<UP: UserPresence, T: TrussedRequirements> Authenticator for crate::Authenti
self.state
.reset_retries(&mut self.trussed)
.map_err(|_| Error::Other)?;

ctap2::client_pin::Response {
key_agreement: None,
pin_token: None,
retries: None,
}
}

Subcommand::ChangePin => {
Expand Down Expand Up @@ -792,83 +780,162 @@ impl<UP: UserPresence, T: TrussedRequirements> Authenticator for crate::Authenti
for pin_protocol in self.pin_protocols() {
self.pin_protocol(*pin_protocol).reset_pin_token();
}

ctap2::client_pin::Response {
key_agreement: None,
pin_token: None,
retries: None,
}
}

// § 6.5.5.7.1 No 4
Subcommand::GetPinToken => {
debug_now!("CTAP2.Pin.GetPinToken");

// 1. check mandatory parameters
let platform_kek = match parameters.key_agreement.as_ref() {
Some(key) => key,
None => {
return Err(Error::MissingParameter);
}
};
let pin_hash_enc = match parameters.pin_hash_enc.as_ref() {
Some(hash) => hash,
None => {
return Err(Error::MissingParameter);
}
};
// 1. Check mandatory parameters
let key_agreement = parameters
.key_agreement
.as_ref()
.ok_or(Error::MissingParameter)?;
let pin_hash_enc = parameters
.pin_hash_enc
.as_ref()
.ok_or(Error::MissingParameter)?;

// 2. fail if no retries left
// 2. Check PIN protocol
let pin_protocol = self.parse_pin_protocol(parameters.pin_protocol)?;

// 3. + 4. Check invalid parameters
if parameters.permissions.is_some() || parameters.rp_id.is_some() {
return Err(Error::InvalidParameter);
}

// 5. Check PIN retries
self.state.pin_blocked()?;

// 3. generate shared secret
// 6. Obtain shared secret
let shared_secret = self
.pin_protocol(pin_protocol)
.shared_secret(platform_kek)?;
.shared_secret(key_agreement)?;

// 7. Request user consent using display -- skipped

// 4. decrement retires
// 8. Decrement PIN retries
self.state.decrement_retries(&mut self.trussed)?;

// 5. decrypt and verify pinHashEnc
// 9. Check PIN
self.decrypt_pin_hash_and_maybe_escalate(
pin_protocol,
&shared_secret,
pin_hash_enc,
)?;

// 6. reset retries
// 10. Reset PIN retries
self.state.reset_retries(&mut self.trussed)?;

// 7. return encrypted pinToken
debug_now!("wrapping pin token");
// info_now!("exists? {}", syscall!(self.trussed.exists(shared_secret)).exists);
// 11. Check forcePINChange -- skipped

// 12. Reset all PIN tokens
for pin_protocol in self.pin_protocols() {
self.pin_protocol(*pin_protocol).reset_pin_token();
}
let pin_token_enc = self
.pin_protocol(pin_protocol)
.encrypt_pin_token(&shared_secret)?;

// 13. Call beginUsingPinUvAuthToken
let mut pin_protocol = self.pin_protocol(pin_protocol);
pin_protocol.begin_using_pin_token(false);

// 14. Assign the default permissions
let mut permissions = Permissions::empty();
permissions.insert(Permissions::MAKE_CREDENTIAL);
permissions.insert(Permissions::GET_ASSERTION);
pin_protocol.restrict_pin_token(permissions, None);

// 15. Return PIN token
response.pin_token = Some(pin_protocol.encrypt_pin_token(&shared_secret)?);

shared_secret.delete(&mut self.trussed);
}

// § 6.5.5.7.2 No 4
Subcommand::GetPinUvAuthTokenUsingPinWithPermissions => {
debug_now!("CTAP2.Pin.GetPinUvAuthTokenUsingPinWithPermissions");

// ble...
if pin_token_enc.len() != 16 {
return Err(Error::Other);
// 1. Check mandatory parameters
let key_agreement = parameters
.key_agreement
.as_ref()
.ok_or(Error::MissingParameter)?;
let pin_hash_enc = parameters
.pin_hash_enc
.as_ref()
.ok_or(Error::MissingParameter)?;
let permissions = parameters.permissions.ok_or(Error::MissingParameter)?;

// 2. Check PIN protocol
let pin_protocol = self.parse_pin_protocol(parameters.pin_protocol)?;

// 3. Check that permissions are not empty
let permissions = Permissions::from_bits_truncate(permissions);
if permissions.is_empty() {
return Err(Error::InvalidParameter);
}

// 4. Check that all requested permissions are supported
let mut unauthorized_permissions = Permissions::empty();
unauthorized_permissions.insert(Permissions::BIO_ENROLLMENT);
if !self.config.supports_large_blobs() {
unauthorized_permissions.insert(Permissions::LARGE_BLOB_WRITE);
}
unauthorized_permissions.insert(Permissions::AUTHENTICATOR_CONFIGURATION);
if permissions.intersects(unauthorized_permissions) {
return Err(Error::UnauthorizedPermission);
}

ctap2::client_pin::Response {
key_agreement: None,
pin_token: Some(pin_token_enc),
retries: None,
// 5. Check PIN retries
self.state.pin_blocked()?;

// 6. Obtain shared secret
let shared_secret = self
.pin_protocol(pin_protocol)
.shared_secret(key_agreement)?;

// 7. Request user consent using display -- skipped

// 8. Decrement PIN retries
self.state.decrement_retries(&mut self.trussed)?;

// 9. Check PIN
self.decrypt_pin_hash_and_maybe_escalate(
pin_protocol,
&shared_secret,
pin_hash_enc,
)?;

// 10. Reset PIN retries
self.state.reset_retries(&mut self.trussed)?;

// 11. Check forcePINChange -- skipped

// 12. Reset all PIN tokens
for pin_protocol in self.pin_protocols() {
self.pin_protocol(*pin_protocol).reset_pin_token();
}

// 13. Call beginUsingPinUvAuthToken
let mut pin_protocol = self.pin_protocol(pin_protocol);
pin_protocol.begin_using_pin_token(false);

// 14. Assign the requested permissions
// 15. Assign the requested RP id
pin_protocol.restrict_pin_token(permissions, parameters.rp_id.clone());

// 16. Return PIN token
response.pin_token = Some(pin_protocol.encrypt_pin_token(&shared_secret)?);

shared_secret.delete(&mut self.trussed);
}

Subcommand::GetPinUvAuthTokenUsingUvWithPermissions
| Subcommand::GetUVRetries
| Subcommand::GetPinUvAuthTokenUsingPinWithPermissions => {
Subcommand::GetPinUvAuthTokenUsingUvWithPermissions | Subcommand::GetUVRetries => {
// todo!("not implemented yet")
return Err(Error::InvalidParameter);
}
})
}

Ok(response)
}

#[inline(never)]
Expand All @@ -880,7 +947,8 @@ impl<UP: UserPresence, T: TrussedRequirements> Authenticator for crate::Authenti
use ctap2::credential_management::Subcommand;

// TODO: I see "failed pinauth" output, but then still continuation...
self.verify_pin_auth_using_token(parameters)?;
// TODO: determine rp_id
self.verify_pin_auth_using_token(parameters, None)?;

let mut cred_mgmt = cm::CredentialManagement::new(self);
let sub_parameters = &parameters.sub_command_params;
Expand Down Expand Up @@ -920,6 +988,9 @@ impl<UP: UserPresence, T: TrussedRequirements> Authenticator for crate::Authenti
.ok_or(Error::MissingParameter)?,
)
}

// 0x7
Subcommand::UpdateUserInformation => Err(Error::InvalidParameter),
}
}

Expand Down Expand Up @@ -949,6 +1020,8 @@ impl<UP: UserPresence, T: TrussedRequirements> Authenticator for crate::Authenti
parameters.pin_auth.map(AsRef::as_ref),
parameters.pin_protocol,
parameters.client_data_hash.as_ref(),
Permissions::GET_ASSERTION,
&parameters.rp_id,
) {
Ok(b) => b,
Err(Error::PinRequired) => {
Expand Down Expand Up @@ -1256,6 +1329,7 @@ impl<UP: UserPresence, T: TrussedRequirements> crate::Authenticator<UP, T> {
fn verify_pin_auth_using_token(
&mut self,
parameters: &ctap2::credential_management::Request,
rp_id: Option<&str>,
) -> Result<()> {
// info_now!("CM params: {:?}", parameters);
use ctap2::credential_management::Subcommand;
Expand Down Expand Up @@ -1297,12 +1371,11 @@ impl<UP: UserPresence, T: TrussedRequirements> crate::Authenticator<UP, T> {
.as_ref()
.ok_or(Error::MissingParameter)?;

if self
.pin_protocol(pin_protocol)
.verify_pin_token(&data[..len], pin_auth)
.is_ok()
{
let mut pin_protocol = self.pin_protocol(pin_protocol);
if let Ok(pin_token) = pin_protocol.verify_pin_token(&data[..len], pin_auth) {
info_now!("passed pinauth");
pin_token.require_permissions(Permissions::CREDENTIAL_MANAGEMENT)?;
pin_token.require_valid_for_rp_id(rp_id)?;
Ok(())
} else {
info_now!("failed pinauth!");
Expand All @@ -1322,6 +1395,9 @@ impl<UP: UserPresence, T: TrussedRequirements> crate::Authenticator<UP, T> {
// of already checked CredMgmt subcommands
Subcommand::EnumerateRpsGetNextRp
| Subcommand::EnumerateCredentialsGetNextCredential => Ok(()),

// not implemented
Subcommand::UpdateUserInformation => Err(Error::InvalidParameter),
}
}

Expand All @@ -1332,6 +1408,8 @@ impl<UP: UserPresence, T: TrussedRequirements> crate::Authenticator<UP, T> {
pin_auth: Option<&[u8]>,
pin_protocol: Option<u32>,
data: &[u8],
permissions: Permissions,
rp_id: &str,
) -> Result<bool> {
// 1. pinAuth zero length -> wait for user touch, then
// return PinNotSet if not set, PinInvalid if set
Expand Down Expand Up @@ -1385,8 +1463,10 @@ impl<UP: UserPresence, T: TrussedRequirements> crate::Authenticator<UP, T> {
// 5. if pinAuth is present and pinProtocol = 1, verify
// success --> set uv = 1
// error --> PinAuthInvalid
self.pin_protocol(pin_protocol)
.verify_pin_token(data, pin_auth)?;
let mut pin_protocol = self.pin_protocol(pin_protocol);
let pin_token = pin_protocol.verify_pin_token(data, pin_auth)?;
pin_token.require_permissions(permissions)?;
pin_token.require_valid_for_rp_id(Some(rp_id))?;

return Ok(true);
} else {
Expand Down Expand Up @@ -1885,8 +1965,9 @@ impl<UP: UserPresence, T: TrussedRequirements> crate::Authenticator<UP, T> {
// SHA-256(data)
auth_data.extend_from_slice(&Sha256::digest(data)).unwrap();

self.pin_protocol(pin_protocol)
.verify_pin_token(&pin_auth, &auth_data)?;
let mut pin_protocol = self.pin_protocol(pin_protocol);
let pin_token = pin_protocol.verify_pin_token(&pin_auth, &auth_data)?;
pin_token.require_permissions(Permissions::LARGE_BLOB_WRITE)?;
}

// 6. Validate data length
Expand Down
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