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126 lines
4.3 KiB
C
126 lines
4.3 KiB
C
#ifndef THIRD_PARTY_NEARBY_PRESENCE_IMPLEMENTATION_NP_LDT_H_
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#define THIRD_PARTY_NEARBY_PRESENCE_IMPLEMENTATION_NP_LDT_H_
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// Copyright 2022 Google LLC
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// https://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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// C API for Rust implementation of LDT [1], tailored to Nearby Presence's
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// BLE 4.2 legacy format advertisement parsing usecase.
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//
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// [1] https://eprint.iacr.org/2017/841.pdf
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#ifdef __cplusplus
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extern "C" {
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#endif
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#include <stddef.h>
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#include <stdint.h>
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// Individual encrypt/decrypt API, useful when creating advertisements or when
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// decrypting advertisements from a known origin
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// The allocated handle to use for encryption
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typedef struct {
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uint64_t handle;
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} NpLdtEncryptHandle;
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// The allocated handle to use for decryption
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typedef struct {
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uint64_t handle;
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} NpLdtDecryptHandle;
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// Key material from the Nearby Presence credential from which keys will be
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// derived.
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typedef struct {
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uint8_t bytes[32];
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} NpLdtKeySeed;
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typedef struct {
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uint8_t bytes[32];
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} NpMetadataKeyHmac;
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typedef struct {
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uint8_t bytes[2];
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} NpLdtSalt;
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// Possible result codes returned from the LDT NP API's
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typedef enum {
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// Call to api was succesful
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NP_LDT_SUCCESS = 0,
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// Payload of invalid length was provided must be >= 16 and <=31 bytes
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NP_LDT_ERROR_INVALID_LENGTH = -1,
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// The provided metadata hmac did not match the calculated hmac on call to
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// decrypt and verify
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NP_LDT_ERROR_MAC_MISMATCH = -2,
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} NP_LDT_RESULT;
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// Allocate an LDT-XTS-AES128 Decryption cipher using the "swap" mix function.
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//
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// `key_seed` is the key material from the Nearby Presence credential from which
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// the LDT key will be derived.
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// 'hmac_tag' is the hmac auth tag calculated on the metadata key used to verify
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// decryption was successful
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//
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// Returns 0 on error, or a non-zero handle on success.
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NpLdtDecryptHandle NpLdtDecryptCreate(NpLdtKeySeed key_seed,
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NpMetadataKeyHmac hmac_tag);
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// Allocate an LDT-XTS-AES128 Encryption cipher using the "swap" mix function.
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//
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// `key_seed` is the key material from the Nearby Presence credential from which
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// the LDT key will be derived.
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//
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// Returns 0 on error, or a non-zero handle on success.
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NpLdtEncryptHandle NpLdtEncryptCreate(NpLdtKeySeed key_seed);
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// Release allocated resources for an NpLdtEncryptHandle
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//
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// Returns 0 on success or an NP_LDT_RESULT error code on failure
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NP_LDT_RESULT NpLdtEncryptClose(NpLdtEncryptHandle handle);
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// Release allocated resources for an NpLdtDecryptHandle
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//
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// Returns 0 on success or an NP_LDT_RESULT error code on failure
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NP_LDT_RESULT NpLdtDecryptClose(NpLdtDecryptHandle handle);
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// Encrypt a 16-31 byte buffer in-place.
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//
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// `buffer` is a pointer to a 16-31 byte plaintext, with length in `buffer_len`.
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// `salt` is the big-endian 2 byte salt that will be used in the Nearby
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// Presence advertisement, which will be incorporated into the tweaks LDT uses
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// while encrypting.
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//
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// Returns 0 on success, in which case `buffer` will now contain ciphertext.
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// Returns an NP_LDT_RESULT error code on failure
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NP_LDT_RESULT NpLdtEncrypt(NpLdtEncryptHandle handle, uint8_t* buffer,
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size_t buffer_len, NpLdtSalt salt);
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// Decrypt a 16-31 byte buffer in-place.
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//
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// `buffer` is a pointer to a 16-31 byte ciphertext, with length in
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// `buffer_len`.
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// `salt` is the big-endian 2 byte salt found in the Nearby Presence
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// advertisement, which will be incorporated into the tweaks LDT uses while
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// decrypting.
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//
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// Returns 0 on success, in which case `buffer` will now contain plaintext.
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// Returns an NP_LDT_RESULT error code on failure
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NP_LDT_RESULT NpLdtDecryptAndVerify(NpLdtDecryptHandle handle, uint8_t* buffer,
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size_t buffer_len, NpLdtSalt salt);
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#ifdef __cplusplus
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} // extern "C"
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#endif
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#endif // THIRD_PARTY_NEARBY_PRESENCE_IMPLEMENTATION_NP_LDT_H_
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