| // Copyright 2021 Google LLC |
| // |
| // 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 |
| // |
| // https://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. |
| |
| // For more information on the Android Profile for DICE, see docs/android.md. |
| |
| #include "dice/android.h" |
| |
| #include <string.h> |
| |
| #include "dice/cbor_reader.h" |
| #include "dice/cbor_writer.h" |
| #include "dice/dice.h" |
| #include "dice/ops.h" |
| #include "dice/ops/trait/cose.h" |
| |
| // Completely gratuitous bit twiddling. |
| static size_t PopulationCount(uint32_t n) { |
| n = n - ((n >> 1) & 0x55555555); |
| n = (n & 0x33333333) + ((n >> 2) & 0x33333333); |
| return (((n + (n >> 4)) & 0x0F0F0F0F) * 0x01010101) >> 24; |
| } |
| |
| DiceResult DiceAndroidFormatConfigDescriptor( |
| const DiceAndroidConfigValues* config_values, size_t buffer_size, |
| uint8_t* buffer, size_t* actual_size) { |
| static const int64_t kComponentNameLabel = -70002; |
| static const int64_t kComponentVersionLabel = -70003; |
| static const int64_t kResettableLabel = -70004; |
| static const int64_t kSecurityVersion = -70005; |
| |
| // AndroidConfigDescriptor = { |
| // ? -70002 : tstr, ; Component name |
| // ? -70003 : int, ; Component version |
| // ? -70004 : null, ; Resettable |
| // } |
| struct CborOut out; |
| CborOutInit(buffer, buffer_size, &out); |
| CborWriteMap(PopulationCount(config_values->configs), &out); |
| if (config_values->configs & DICE_ANDROID_CONFIG_COMPONENT_NAME && |
| config_values->component_name) { |
| CborWriteInt(kComponentNameLabel, &out); |
| CborWriteTstr(config_values->component_name, &out); |
| } |
| if (config_values->configs & DICE_ANDROID_CONFIG_COMPONENT_VERSION) { |
| CborWriteInt(kComponentVersionLabel, &out); |
| CborWriteUint(config_values->component_version, &out); |
| } |
| if (config_values->configs & DICE_ANDROID_CONFIG_RESETTABLE) { |
| CborWriteInt(kResettableLabel, &out); |
| CborWriteNull(&out); |
| } |
| if (config_values->configs & DICE_ANDROID_CONFIG_SECURITY_VERSION) { |
| CborWriteInt(kSecurityVersion, &out); |
| CborWriteUint(config_values->security_version, &out); |
| } |
| *actual_size = CborOutSize(&out); |
| if (CborOutOverflowed(&out)) { |
| return kDiceResultBufferTooSmall; |
| } |
| return kDiceResultOk; |
| } |
| |
| DiceResult DiceAndroidMainFlow(void* context, |
| const uint8_t current_cdi_attest[DICE_CDI_SIZE], |
| const uint8_t current_cdi_seal[DICE_CDI_SIZE], |
| const uint8_t* chain, size_t chain_size, |
| const DiceInputValues* input_values, |
| size_t buffer_size, uint8_t* buffer, |
| size_t* actual_size, |
| uint8_t next_cdi_attest[DICE_CDI_SIZE], |
| uint8_t next_cdi_seal[DICE_CDI_SIZE]) { |
| DiceResult result; |
| enum CborReadResult res; |
| struct CborIn in; |
| size_t chain_item_count; |
| |
| // The Android DICE chain has a more detailed internal structure, but those |
| // details aren't relevant to the work of this function. |
| // |
| // DiceCertChain = [ |
| // COSE_Key, ; Root public key |
| // + COSE_Sign1, ; DICE chain entries |
| // ] |
| CborInInit(chain, chain_size, &in); |
| res = CborReadArray(&in, &chain_item_count); |
| if (res != CBOR_READ_RESULT_OK) { |
| return kDiceResultInvalidInput; |
| } |
| |
| if (chain_item_count < 2 || chain_item_count == SIZE_MAX) { |
| // There should at least be the public key and one entry. |
| return kDiceResultInvalidInput; |
| } |
| |
| // Measure the existing chain entries. |
| size_t chain_items_offset = CborInOffset(&in); |
| for (size_t chain_pos = 0; chain_pos < chain_item_count; ++chain_pos) { |
| res = CborReadSkip(&in); |
| if (res != CBOR_READ_RESULT_OK) { |
| return kDiceResultInvalidInput; |
| } |
| } |
| size_t chain_items_size = CborInOffset(&in) - chain_items_offset; |
| |
| // Copy to the new buffer, with space in the chain for one more entry. |
| struct CborOut out; |
| CborOutInit(buffer, buffer_size, &out); |
| CborWriteArray(chain_item_count + 1, &out); |
| if (CborOutOverflowed(&out) || |
| chain_items_size > buffer_size - CborOutSize(&out)) { |
| // Continue with an empty buffer to measure the required size. |
| buffer_size = 0; |
| } else { |
| memcpy(buffer + CborOutSize(&out), chain + chain_items_offset, |
| chain_items_size); |
| buffer += CborOutSize(&out) + chain_items_size; |
| buffer_size -= CborOutSize(&out) + chain_items_size; |
| } |
| |
| size_t certificate_size; |
| result = DiceMainFlow(context, current_cdi_attest, current_cdi_seal, |
| input_values, buffer_size, buffer, &certificate_size, |
| next_cdi_attest, next_cdi_seal); |
| *actual_size = CborOutSize(&out) + chain_items_size + certificate_size; |
| return result; |
| } |
| |
| static DiceResult DiceAndroidMainFlowWithNewDiceChain( |
| void* context, const uint8_t current_cdi_attest[DICE_CDI_SIZE], |
| const uint8_t current_cdi_seal[DICE_CDI_SIZE], |
| const DiceInputValues* input_values, size_t buffer_size, uint8_t* buffer, |
| size_t* chain_size, uint8_t next_cdi_attest[DICE_CDI_SIZE], |
| uint8_t next_cdi_seal[DICE_CDI_SIZE]) { |
| uint8_t current_cdi_private_key_seed[DICE_PRIVATE_KEY_SEED_SIZE]; |
| uint8_t attestation_public_key[DICE_PUBLIC_KEY_SIZE]; |
| uint8_t attestation_private_key[DICE_PRIVATE_KEY_SIZE]; |
| // Derive an asymmetric private key seed from the current attestation CDI |
| // value. |
| DiceResult result = DiceDeriveCdiPrivateKeySeed(context, current_cdi_attest, |
| current_cdi_private_key_seed); |
| if (result != kDiceResultOk) { |
| goto out; |
| } |
| // Derive attestation key pair. |
| result = DiceKeypairFromSeed(context, current_cdi_private_key_seed, |
| attestation_public_key, attestation_private_key); |
| if (result != kDiceResultOk) { |
| goto out; |
| } |
| |
| // Consruct the DICE chain from the attestation public key and the next CDI |
| // certificate. |
| struct CborOut out; |
| CborOutInit(buffer, buffer_size, &out); |
| CborWriteArray(2, &out); |
| size_t encoded_size_used = CborOutSize(&out); |
| if (CborOutOverflowed(&out)) { |
| // Continue with an empty buffer to measure the required size. |
| buffer_size = 0; |
| } else { |
| buffer += encoded_size_used; |
| buffer_size -= encoded_size_used; |
| } |
| |
| size_t encoded_pub_key_size = 0; |
| result = DiceCoseEncodePublicKey(context, attestation_public_key, buffer_size, |
| buffer, &encoded_pub_key_size); |
| if (result == kDiceResultOk) { |
| buffer += encoded_pub_key_size; |
| buffer_size -= encoded_pub_key_size; |
| } else if (result == kDiceResultBufferTooSmall) { |
| // Continue with an empty buffer to measure the required size. |
| buffer_size = 0; |
| } else { |
| goto out; |
| } |
| |
| result = DiceMainFlow(context, current_cdi_attest, current_cdi_seal, |
| input_values, buffer_size, buffer, chain_size, |
| next_cdi_attest, next_cdi_seal); |
| *chain_size += encoded_size_used + encoded_pub_key_size; |
| if (result != kDiceResultOk) { |
| return result; |
| } |
| |
| out: |
| DiceClearMemory(context, sizeof(current_cdi_private_key_seed), |
| current_cdi_private_key_seed); |
| DiceClearMemory(context, sizeof(attestation_private_key), |
| attestation_private_key); |
| |
| return result; |
| } |
| |
| // AndroidDiceHandover = { |
| // 1 : bstr .size 32, ; CDI_Attest |
| // 2 : bstr .size 32, ; CDI_Seal |
| // ? 3 : DiceCertChain, ; Android DICE chain |
| // } |
| static const int64_t kCdiAttestLabel = 1; |
| static const int64_t kCdiSealLabel = 2; |
| static const int64_t kDiceChainLabel = 3; |
| |
| DiceResult DiceAndroidHandoverMainFlow(void* context, const uint8_t* handover, |
| size_t handover_size, |
| const DiceInputValues* input_values, |
| size_t buffer_size, uint8_t* buffer, |
| size_t* actual_size) { |
| DiceResult result; |
| const uint8_t* current_cdi_attest; |
| const uint8_t* current_cdi_seal; |
| const uint8_t* chain; |
| size_t chain_size; |
| |
| result = |
| DiceAndroidHandoverParse(handover, handover_size, ¤t_cdi_attest, |
| ¤t_cdi_seal, &chain, &chain_size); |
| if (result != kDiceResultOk) { |
| return kDiceResultInvalidInput; |
| } |
| |
| // Write the new handover data. |
| struct CborOut out; |
| CborOutInit(buffer, buffer_size, &out); |
| CborWriteMap(/*num_pairs=*/3, &out); |
| CborWriteInt(kCdiAttestLabel, &out); |
| uint8_t* next_cdi_attest = CborAllocBstr(DICE_CDI_SIZE, &out); |
| CborWriteInt(kCdiSealLabel, &out); |
| uint8_t* next_cdi_seal = CborAllocBstr(DICE_CDI_SIZE, &out); |
| CborWriteInt(kDiceChainLabel, &out); |
| |
| uint8_t ignored_cdi_attest[DICE_CDI_SIZE]; |
| uint8_t ignored_cdi_seal[DICE_CDI_SIZE]; |
| if (CborOutOverflowed(&out)) { |
| // Continue with an empty buffer and placeholders for the output CDIs to |
| // measure the required size. |
| buffer_size = 0; |
| next_cdi_attest = ignored_cdi_attest; |
| next_cdi_seal = ignored_cdi_seal; |
| } else { |
| buffer += CborOutSize(&out); |
| buffer_size -= CborOutSize(&out); |
| } |
| |
| if (chain_size != 0) { |
| // If the DICE chain is present in the handover, append the next certificate |
| // to the existing DICE chain. |
| result = DiceAndroidMainFlow(context, current_cdi_attest, current_cdi_seal, |
| chain, chain_size, input_values, buffer_size, |
| buffer, &chain_size, next_cdi_attest, |
| next_cdi_seal); |
| } else { |
| // If DICE chain is not present in the handover, construct the DICE chain |
| // from the public key derived from the current CDI attest and the next CDI |
| // certificate. |
| result = DiceAndroidMainFlowWithNewDiceChain( |
| context, current_cdi_attest, current_cdi_seal, input_values, |
| buffer_size, buffer, &chain_size, next_cdi_attest, next_cdi_seal); |
| } |
| *actual_size = CborOutSize(&out) + chain_size; |
| return result; |
| } |
| |
| DiceResult DiceAndroidHandoverParse(const uint8_t* handover, |
| size_t handover_size, |
| const uint8_t** cdi_attest, |
| const uint8_t** cdi_seal, |
| const uint8_t** chain, size_t* chain_size) { |
| // Extract details from the handover data. |
| struct CborIn in; |
| int64_t label; |
| size_t num_pairs; |
| size_t item_size; |
| CborInInit(handover, handover_size, &in); |
| if (CborReadMap(&in, &num_pairs) != CBOR_READ_RESULT_OK || num_pairs < 2 || |
| // Read the attestation CDI. |
| CborReadInt(&in, &label) != CBOR_READ_RESULT_OK || |
| label != kCdiAttestLabel || |
| CborReadBstr(&in, &item_size, cdi_attest) != CBOR_READ_RESULT_OK || |
| item_size != DICE_CDI_SIZE || |
| // Read the sealing CDI. |
| CborReadInt(&in, &label) != CBOR_READ_RESULT_OK || |
| label != kCdiSealLabel || |
| CborReadBstr(&in, &item_size, cdi_seal) != CBOR_READ_RESULT_OK || |
| item_size != DICE_CDI_SIZE) { |
| return kDiceResultInvalidInput; |
| } |
| |
| *chain = NULL; |
| *chain_size = 0; |
| if (num_pairs >= 3 && CborReadInt(&in, &label) == CBOR_READ_RESULT_OK) { |
| if (label == kDiceChainLabel) { |
| // Calculate the DICE chain size, if it is present in the handover object. |
| size_t chain_start = CborInOffset(&in); |
| if (CborReadSkip(&in) != CBOR_READ_RESULT_OK) { |
| return kDiceResultInvalidInput; |
| } |
| *chain = handover + chain_start; |
| *chain_size = CborInOffset(&in) - chain_start; |
| } |
| } |
| |
| return kDiceResultOk; |
| } |
