| //! Functionality for converting legacy keyblob formats. |
| |
| use alloc::vec::Vec; |
| use kmr_common::keyblob::{ |
| legacy, SecureDeletionData, SecureDeletionSecretManager, SecureDeletionSlot, |
| }; |
| use kmr_common::{ |
| crypto, |
| crypto::{aes, OpaqueKeyMaterial, OpaqueOr}, |
| explicit, get_bool_tag_value, get_opt_tag_value, get_tag_value, keyblob, km_err, tag, |
| try_to_vec, vec_try, Error, FallibleAllocExt, |
| }; |
| use kmr_ta::device; |
| use kmr_wire::{ |
| keymint, |
| keymint::{Algorithm, BootInfo, EcCurve, ErrorCode, KeyParam, KeyPurpose, SecurityLevel}, |
| KeySizeInBits, |
| }; |
| use log::error; |
| |
| /// Prefix for KEK derivation input when secure deletion not supported. |
| const AES_GCM_DESCRIPTOR_V1: &[u8] = b"AES-256-GCM-HKDF-SHA-256, version 1\0"; |
| /// Prefix for KEK derivation input when secure deletion supported. |
| const AES_GCM_DESCRIPTOR_V2: &[u8] = b"AES-256-GCM-HKDF-SHA-256, version 2\0"; |
| |
| /// Slot number used to indicate that a key has no per-key secure deletion data. |
| const NO_SDD_SLOT_IDX: u32 = 0; |
| |
| /// Legacy key handler that detects and converts `EncryptedKeyBlob` instances from |
| /// the previous Trusty implementation of KeyMint/Keymaster. |
| pub struct TrustyLegacyKeyBlobHandler { |
| pub aes: Box<dyn crypto::Aes>, |
| pub hkdf: Box<dyn crypto::Hkdf>, |
| pub sdd_mgr: Option<Box<dyn SecureDeletionSecretManager>>, |
| pub keys: Box<dyn device::RetrieveKeyMaterial>, |
| } |
| |
| impl TrustyLegacyKeyBlobHandler { |
| /// Build the derivation information needed for KEK derivation that is compatible with the |
| /// previous C++ implementation. |
| fn build_derivation_info( |
| &self, |
| encrypted_keyblob: &legacy::EncryptedKeyBlob, |
| hidden: &[KeyParam], |
| sdd_info: Option<(SecureDeletionData, u32)>, |
| ) -> Result<Vec<u8>, Error> { |
| let mut info = if sdd_info.is_some() { |
| try_to_vec(AES_GCM_DESCRIPTOR_V2)? |
| } else { |
| try_to_vec(AES_GCM_DESCRIPTOR_V1)? |
| }; |
| info.try_extend_from_slice(&tag::legacy::serialize(hidden)?)?; |
| info.try_extend_from_slice(&tag::legacy::serialize(&encrypted_keyblob.hw_enforced)?)?; |
| info.try_extend_from_slice(&tag::legacy::serialize(&encrypted_keyblob.sw_enforced)?)?; |
| if let Some((sdd_data, slot)) = sdd_info { |
| info.try_extend_from_slice( |
| &(sdd_data.factory_reset_secret.len() as u32).to_ne_bytes(), |
| )?; |
| info.try_extend_from_slice(&sdd_data.factory_reset_secret)?; |
| |
| // If the slot is zero, the per-key secret is empty. |
| let secret: &[u8] = if slot == 0 { &[] } else { &sdd_data.secure_deletion_secret }; |
| info.try_extend_from_slice(&(secret.len() as u32).to_ne_bytes())?; |
| info.try_extend_from_slice(secret)?; |
| |
| info.try_extend_from_slice(&slot.to_ne_bytes())?; |
| } |
| Ok(info) |
| } |
| |
| /// Derive the key encryption key for a keyblob. |
| fn derive_kek( |
| &self, |
| root_kek: &OpaqueOr<kmr_common::crypto::hmac::Key>, |
| encrypted_keyblob: &legacy::EncryptedKeyBlob, |
| hidden: &[KeyParam], |
| sdd_data: Option<(SecureDeletionData, u32)>, |
| ) -> Result<crypto::aes::Key, Error> { |
| let info = self.build_derivation_info(encrypted_keyblob, hidden, sdd_data)?; |
| // Trusty uses explicit keys for legacy keyblobs. |
| let raw_key = self.hkdf.hkdf(&[], &explicit!(root_kek)?.0, &info, 256 / 8)?; |
| let aes_key = crypto::aes::Key::Aes256( |
| raw_key.try_into().map_err(|_e| km_err!(UnknownError, "unexpected HKDF output len"))?, |
| ); |
| Ok(aes_key) |
| } |
| |
| /// Convert a keyblob from the legacy C++ format to the current format. |
| fn convert_key( |
| &self, |
| keyblob: &[u8], |
| params: &[KeyParam], |
| root_of_trust: &BootInfo, |
| sec_level: SecurityLevel, |
| ) -> Result<keyblob::PlaintextKeyBlob, Error> { |
| let encrypted_keyblob = legacy::EncryptedKeyBlob::deserialize(keyblob)?; |
| |
| // Find the secure deletion data (if any) for the key. |
| let sdd_info = match ( |
| encrypted_keyblob.format.requires_secure_deletion(), |
| &self.sdd_mgr, |
| encrypted_keyblob.key_slot, |
| ) { |
| (true, Some(sdd_mgr), None) | (true, Some(sdd_mgr), Some(NO_SDD_SLOT_IDX)) => { |
| // Zero slot index implies that just the factory reset secret is populated. |
| let sdd_data = sdd_mgr.get_factory_reset_secret()?; |
| Some((sdd_data, NO_SDD_SLOT_IDX)) |
| } |
| (true, Some(sdd_mgr), Some(slot_idx)) => { |
| let slot = SecureDeletionSlot(slot_idx); |
| let sdd_data = sdd_mgr.get_secret(slot)?; |
| |
| Some((sdd_data, slot_idx)) |
| } |
| (true, None, _) => { |
| return Err(km_err!( |
| InvalidKeyBlob, |
| "keyblob requires secure deletion but no implementation available", |
| )) |
| } |
| (false, _, Some(slot)) => { |
| return Err(km_err!( |
| InvalidKeyBlob, |
| "unexpected SDD slot {} for format {:?}", |
| slot, |
| encrypted_keyblob.format |
| )) |
| } |
| (false, _, None) => None, |
| }; |
| |
| // Convert the key characteristics to current form. |
| let mut characteristics = vec_try![keymint::KeyCharacteristics { |
| security_level: sec_level, |
| authorizations: try_to_vec(&encrypted_keyblob.hw_enforced)?, |
| }]?; |
| if !encrypted_keyblob.sw_enforced.is_empty() { |
| characteristics.try_push(keymint::KeyCharacteristics { |
| security_level: keymint::SecurityLevel::Keystore, |
| authorizations: try_to_vec(&encrypted_keyblob.sw_enforced)?, |
| })?; |
| } |
| |
| // Derive the KEK, using hidden inputs from params and root-of-trust. |
| let rots = &[ |
| &root_of_trust.verified_boot_key[..], |
| &(root_of_trust.verified_boot_state as u32).to_ne_bytes(), |
| &[if root_of_trust.device_boot_locked { 0x01u8 } else { 0x00u8 }], |
| ]; |
| let hidden_params = legacy::hidden(params, rots)?; |
| |
| let rollback_version = match encrypted_keyblob.addl_info { |
| Some(v) => Some( |
| hwkey::OsRollbackVersion::try_from(v) |
| .map_err(|e| km_err!(InvalidKeyBlob, "unexpected addl_info={} : {:?}", v, e))?, |
| ), |
| None => None, |
| }; |
| let kek_context = super::TrustyKekContext::new( |
| encrypted_keyblob.format.is_versioned(), |
| encrypted_keyblob.kdf_version.map(hwkey::KdfVersion::from), |
| rollback_version, |
| )? |
| .to_raw()?; |
| |
| let root_kek = self.keys.root_kek(&kek_context)?; |
| let aes_key = self.derive_kek(&root_kek, &encrypted_keyblob, &hidden_params, sdd_info)?; |
| |
| // Key material is encrypted with AES-GCM; decrypt it. |
| let nonce: [u8; aes::GCM_NONCE_SIZE] = encrypted_keyblob |
| .nonce |
| .try_into() |
| .map_err(|_e| km_err!(InvalidKeyBlob, "unexpected nonce len",))?; |
| let mode = match encrypted_keyblob.tag.len() { |
| 12 => crypto::aes::GcmMode::GcmTag12 { nonce }, |
| 13 => crypto::aes::GcmMode::GcmTag13 { nonce }, |
| 14 => crypto::aes::GcmMode::GcmTag14 { nonce }, |
| 15 => crypto::aes::GcmMode::GcmTag15 { nonce }, |
| 16 => crypto::aes::GcmMode::GcmTag16 { nonce }, |
| l => return Err(km_err!(InvalidKeyBlob, "unexpected AES-GCM tag length {}", l)), |
| }; |
| let mut op = |
| self.aes.begin_aead(aes_key.into(), mode, crypto::SymmetricOperation::Decrypt)?; |
| let mut raw_key_material = op.update(&encrypted_keyblob.ciphertext)?; |
| raw_key_material.try_extend_from_slice(&op.update(&encrypted_keyblob.tag)?)?; |
| raw_key_material.try_extend_from_slice(&op.finish()?)?; |
| if raw_key_material.len() != encrypted_keyblob.ciphertext.len() { |
| return Err(km_err!( |
| UnknownError, |
| "deciphered len {} != encrypted len {}", |
| raw_key_material.len(), |
| encrypted_keyblob.ciphertext.len() |
| )); |
| } |
| |
| // Convert the key material into current form. |
| let chars = &encrypted_keyblob.hw_enforced; |
| let key_material = match get_tag_value!(chars, Algorithm, ErrorCode::InvalidKeyBlob)? { |
| // Symmetric keys have the key material stored as raw bytes. |
| Algorithm::Aes => { |
| // Special case: an AES key might be a storage key. |
| if get_bool_tag_value!(chars, StorageKey)? { |
| // Storage key is opaque data. |
| crypto::KeyMaterial::Aes(OpaqueOr::Opaque(OpaqueKeyMaterial(raw_key_material))) |
| } else { |
| // Normal case: expect explicit AES key material. |
| crypto::KeyMaterial::Aes(crypto::aes::Key::new(raw_key_material)?.into()) |
| } |
| } |
| Algorithm::TripleDes => { |
| crypto::KeyMaterial::TripleDes(crypto::des::Key::new(raw_key_material)?.into()) |
| } |
| Algorithm::Hmac => { |
| crypto::KeyMaterial::Hmac(crypto::hmac::Key::new(raw_key_material).into()) |
| } |
| |
| // RSA keys have key material stored as a PKCS#1 `RSAPrivateKey` structure, DER-encoded, |
| // as decoded by the BoringSSL `RSA_parse_private_key()` function. This matches the |
| // internal form of a [`crypto::rsa::Key`]. |
| Algorithm::Rsa => crypto::KeyMaterial::Rsa(crypto::rsa::Key(raw_key_material).into()), |
| |
| Algorithm::Ec => { |
| // Determine the EC curve, allowing for old keys that don't include `EC_CURVE` tag. |
| let ec_curve = match get_opt_tag_value!(chars, EcCurve)? { |
| Some(c) => *c, |
| None => match get_tag_value!(chars, KeySize, ErrorCode::InvalidKeyBlob)? { |
| KeySizeInBits(224) => EcCurve::P224, |
| KeySizeInBits(384) => EcCurve::P384, |
| KeySizeInBits(256) => { |
| return Err(km_err!(InvalidKeyBlob, "key size 256 ambiguous for EC")) |
| } |
| KeySizeInBits(521) => EcCurve::P521, |
| sz => return Err(km_err!(InvalidKeyBlob, "key size {:?} invalid", sz)), |
| }, |
| }; |
| match ec_curve { |
| // NIST curve EC keys are stored as an `ECPrivateKey` structure, DER-encoded, as |
| // decoded by the BoringSSL `EC_KEY_parse_private_key()` function. This matches |
| // the internal form of a [`crypto::ec::NistKey`]. |
| EcCurve::P224 => crypto::KeyMaterial::Ec( |
| ec_curve, |
| crypto::CurveType::Nist, |
| crypto::ec::Key::P224(crypto::ec::NistKey(raw_key_material)).into(), |
| ), |
| EcCurve::P256 => crypto::KeyMaterial::Ec( |
| ec_curve, |
| crypto::CurveType::Nist, |
| crypto::ec::Key::P256(crypto::ec::NistKey(raw_key_material)).into(), |
| ), |
| EcCurve::P384 => crypto::KeyMaterial::Ec( |
| ec_curve, |
| crypto::CurveType::Nist, |
| crypto::ec::Key::P384(crypto::ec::NistKey(raw_key_material)).into(), |
| ), |
| EcCurve::P521 => crypto::KeyMaterial::Ec( |
| ec_curve, |
| crypto::CurveType::Nist, |
| crypto::ec::Key::P521(crypto::ec::NistKey(raw_key_material)).into(), |
| ), |
| EcCurve::Curve25519 => { |
| let key = crypto::ec::import_pkcs8_key(&raw_key_material)?; |
| if let crypto::KeyMaterial::Ec(EcCurve::Curve25519, curve_type, _ec_key) = |
| &key |
| { |
| match curve_type { |
| crypto::CurveType::Nist => { |
| return Err(km_err!( |
| InvalidKeyBlob, |
| "unexpected NIST key with curve25519" |
| )) |
| } |
| crypto::CurveType::Xdh => { |
| if tag::primary_purpose(chars)? != KeyPurpose::AgreeKey { |
| return Err(km_err!( |
| InvalidKeyBlob, |
| "purpose not AGREE_KEY for X25519 key" |
| )); |
| } |
| } |
| crypto::CurveType::EdDsa => { |
| if tag::primary_purpose(chars)? == KeyPurpose::AgreeKey { |
| return Err(km_err!( |
| InvalidKeyBlob, |
| "AGREE_KEY purpose for non-XDH 25519 key" |
| )); |
| } |
| } |
| } |
| } else { |
| return Err(km_err!( |
| InvalidKeyBlob, |
| "curve25519 key with wrong contents" |
| )); |
| } |
| key |
| } |
| } |
| } |
| }; |
| |
| Ok(keyblob::PlaintextKeyBlob { characteristics, key_material }) |
| } |
| } |
| |
| impl keyblob::LegacyKeyHandler for TrustyLegacyKeyBlobHandler { |
| fn convert_legacy_key( |
| &self, |
| keyblob: &[u8], |
| params: &[KeyParam], |
| root_of_trust: &BootInfo, |
| sec_level: SecurityLevel, |
| ) -> Result<keyblob::PlaintextKeyBlob, Error> { |
| self.convert_key(keyblob, params, root_of_trust, sec_level) |
| } |
| |
| fn delete_legacy_key(&mut self, keyblob: &[u8]) -> Result<(), Error> { |
| let encrypted_keyblob = legacy::EncryptedKeyBlob::deserialize(keyblob)?; |
| if let Some(slot) = encrypted_keyblob.key_slot { |
| if slot != NO_SDD_SLOT_IDX { |
| if !encrypted_keyblob.format.requires_secure_deletion() { |
| return Err(km_err!( |
| UnknownError, |
| "legacy keyblob of non-SDD format {:?} has non-empty SDD slot {:?}!", |
| encrypted_keyblob.format, |
| slot |
| )); |
| } |
| if let Some(sdd_mgr) = self.sdd_mgr.as_mut() { |
| if let Err(e) = sdd_mgr.delete_secret(SecureDeletionSlot(slot)) { |
| error!("failed to delete SDD slot {:?} for legacy key: {:?}", slot, e); |
| } |
| } else { |
| error!("legacy key has SDD slot {:?} but no SDD mgr available!", slot); |
| } |
| } |
| } |
| Ok(()) |
| } |
| } |
