| /* |
| * Copyright 2015 The Android Open Source Project |
| * |
| * Licensed under the Apache License, Version 2.0 (the "License"); |
| * you may not use this file except in compliance with the License. |
| * You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| |
| #include "auth_encrypted_key_blob.h" |
| |
| #include <keymaster/android_keymaster_utils.h> |
| #include <keymaster/authorization_set.h> |
| #include <keymaster/logger.h> |
| |
| #include "ocb_utils.h" |
| |
| namespace keymaster { |
| |
| const uint32_t CURRENT_BLOB_VERSION = 0; |
| |
| keymaster_error_t SerializeAuthEncryptedBlob(const KeymasterKeyBlob& encrypted_key_material, |
| const AuthorizationSet& hw_enforced, |
| const AuthorizationSet& sw_enforced, |
| |
| const Buffer& nonce, const Buffer& tag, |
| KeymasterKeyBlob* key_blob) { |
| size_t size = 1 /* version byte */ + nonce.SerializedSize() + |
| encrypted_key_material.SerializedSize() + tag.SerializedSize() + |
| hw_enforced.SerializedSize() + sw_enforced.SerializedSize(); |
| |
| if (!key_blob->Reset(size)) |
| return KM_ERROR_MEMORY_ALLOCATION_FAILED; |
| |
| uint8_t* buf = key_blob->writable_data(); |
| const uint8_t* end = key_blob->key_material + key_blob->key_material_size; |
| |
| *buf++ = CURRENT_BLOB_VERSION; |
| buf = nonce.Serialize(buf, end); |
| buf = encrypted_key_material.Serialize(buf, end); |
| buf = tag.Serialize(buf, end); |
| buf = hw_enforced.Serialize(buf, end); |
| buf = sw_enforced.Serialize(buf, end); |
| if (buf != key_blob->key_material + key_blob->key_material_size) |
| return KM_ERROR_UNKNOWN_ERROR; |
| |
| return KM_ERROR_OK; |
| } |
| |
| static keymaster_error_t DeserializeUnversionedBlob(const KeymasterKeyBlob& key_blob, |
| KeymasterKeyBlob* encrypted_key_material, |
| AuthorizationSet* hw_enforced, |
| AuthorizationSet* sw_enforced, Buffer* nonce, |
| Buffer* tag) { |
| const uint8_t* tmp = key_blob.key_material; |
| const uint8_t** buf_ptr = &tmp; |
| const uint8_t* end = tmp + key_blob.key_material_size; |
| |
| if (!nonce->reserve(OCB_NONCE_LENGTH) || !tag->reserve(OCB_TAG_LENGTH)) |
| return KM_ERROR_MEMORY_ALLOCATION_FAILED; |
| |
| if (!copy_from_buf(buf_ptr, end, nonce->peek_write(), OCB_NONCE_LENGTH) || |
| !encrypted_key_material->Deserialize(buf_ptr, end) || |
| !copy_from_buf(buf_ptr, end, tag->peek_write(), OCB_TAG_LENGTH) || |
| !hw_enforced->Deserialize(buf_ptr, end) || // |
| !sw_enforced->Deserialize(buf_ptr, end)) { |
| LOG_D("Failed to deserialize unversioned blob (may be a HW-backed key)", 0); |
| return KM_ERROR_INVALID_KEY_BLOB; |
| } |
| if (!nonce->advance_write(OCB_NONCE_LENGTH) || !tag->advance_write(OCB_TAG_LENGTH)) |
| return KM_ERROR_UNKNOWN_ERROR; |
| return KM_ERROR_OK; |
| } |
| |
| keymaster_error_t DeserializeAuthEncryptedBlob(const KeymasterKeyBlob& key_blob, |
| KeymasterKeyBlob* encrypted_key_material, |
| AuthorizationSet* hw_enforced, |
| AuthorizationSet* sw_enforced, Buffer* nonce, |
| Buffer* tag) { |
| if (!key_blob.key_material || key_blob.key_material_size == 0) |
| return KM_ERROR_INVALID_KEY_BLOB; |
| |
| const uint8_t* tmp = key_blob.key_material; |
| const uint8_t** buf_ptr = &tmp; |
| const uint8_t* end = tmp + key_blob.key_material_size; |
| |
| if (end <= *buf_ptr) |
| return KM_ERROR_INVALID_KEY_BLOB; |
| |
| uint8_t version = *(*buf_ptr)++; |
| if (version != CURRENT_BLOB_VERSION || // |
| !nonce->Deserialize(buf_ptr, end) || nonce->available_read() != OCB_NONCE_LENGTH || |
| !encrypted_key_material->Deserialize(buf_ptr, end) || // |
| !tag->Deserialize(buf_ptr, end) || tag->available_read() != OCB_TAG_LENGTH || |
| !hw_enforced->Deserialize(buf_ptr, end) || // |
| !sw_enforced->Deserialize(buf_ptr, end)) { |
| // This blob failed to parse. Either it's corrupted or it's a blob generated by an earlier |
| // version of keymaster using a previous blob format which did not include the version byte |
| // or the nonce or tag length fields. So we try to parse it as that previous version. |
| // |
| // Note that it's not really a problem if we erronously parse a corrupted blob, because |
| // decryption will fail the authentication check. |
| // |
| // A bigger potential problem is: What if a valid unversioned blob appears to parse |
| // correctly as a versioned blob? It would then be rejected during decryption, causing a |
| // valid key to become unusable. If this is a disk encryption key, upgrading to a keymaster |
| // version with the new format would destroy the user's data. |
| // |
| // What is the probability that an unversioned key could be successfully parsed as a version |
| // 0 key? The first 12 bytes of an unversioned key are the nonce, which, in the only |
| // keymaster version released with unversioned keys, is chosen randomly. In order for an |
| // unversioned key to parse as a version 0 key, the following must be true about the first |
| // five of those random bytes: |
| // |
| // 1. The first byte must be zero. This will happen with probability 1/2^8. |
| // |
| // 2. The second through fifth bytes must contain an unsigned integer value equal to |
| // NONCE_LENGTH. This will happen with probability 1/2^32. |
| // |
| // Based on those two checks alone, the probability of interpreting an unversioned blob as a |
| // version 0 blob is 1/2^40. That's small enough to be negligible, but there are additional |
| // checks which lower it further. |
| LOG_D("Failed to deserialize versioned key blob. Assuming unversioned.", 0); |
| return DeserializeUnversionedBlob(key_blob, encrypted_key_material, hw_enforced, |
| sw_enforced, nonce, tag); |
| } |
| return KM_ERROR_OK; |
| } |
| |
| } // namespace keymaster |