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(456) 0x01. Blockchain - Data structures

Specializations > System programming & Algorithm > Blockchain

Project author

Alexandre Gautier

Assignment dates

07-26-2021 to 08-04-2021

Description

Introduction to data structures used to store each block's info profile and payload of data.

Provided file(s)

provided/ (all originally here):

test/:

Mandatory Tasks

✅ 0. Create blockchain

Write a function that creates a blockchain structure, and initializes it.

  • Prototype: blockchain_t *blockchain_create(void);
  • The blockchain must contain one block upon creation. This block is called the Genesis Block. Its content is static, and pre-defined as follows:
    • index -> 0
    • difficulty -> 0
    • timestamp -> 1537578000
    • nonce -> 0
    • prev_hash -> 0 (times 32)
    • data -> "Holberton School" (16 bytes long)
    • hash -> c52c26c8b5461639635d8edf2a97d48d0c8e0009c817f2b1d3d7ff2f04515803

File(s): blockchain_create.c
Compiled: gcc -Wall -Wextra -Werror -pedantic -I. -o blockchain_create-test blockchain_create.c test/blockchain_create-main.c provided/_blockchain_print.c provided/_blockchain_destroy.c -L../../crypto -lhblk_crypto -lllist -lssl -lcrypto -pthread

✅ 1. Create block

Write a function that creates a block structure and initializes it.

  • Prototype: block_t *block_create(block_t const *prev, int8_t const *data, uint32_t data_len);, where:
    • prev is a pointer to the previous block in the blockchain
    • data points to a memory area to duplicate in the block’s data
    • data_len stores the number of bytes to duplicate in data. If data_len is bigger than BLOCKCHAIN_DATA_MAX, then only BLOCKCHAIN_DATA_MAX bytes must be duplicated.
    • The new block’s index must be the previous block’s index + 1
    • The new block’s difficulty and nonce must both be initialized to 0
    • The new block’s timestamp should be initialized using the time(2) system call. It is normal if your value differs from the following example.
    • The new block’s hash must be zeroed
  • Your function must return a pointer to the allocated block

File(s): block_create.c
Compiled: gcc -Wall -Wextra -Werror -pedantic -I. -o block_create-test blockchain_create.c block_create.c test/block_create-main.c provided/_blockchain_print.c provided/_blockchain_destroy.c -L../../crypto -lhblk_crypto -lllist -lssl -lcrypto -pthread

✅ 2. Delete block

Write a function that deletes an existing block

  • Prototype: void block_destroy(block_t *block);, where:
    • block points to the block to delete

File(s): block_destroy.c
Compiled: gcc -Wall -Wextra -Werror -pedantic -I. -o block_destroy-test blockchain_create.c block_create.c block_destroy.c test/block_destroy-main.c provided/_blockchain_destroy.c -L../../crypto -lhblk_crypto -lllist -lssl -lcrypto -pthread

✅ 3. Delete blockchain

Write a function that deletes an existing blockchain, along with all the blocks it contains

  • Prototype: void blockchain_destroy(blockchain_t *blockchain);, where:
    • blockchain points to the blockchain structure to delete
  • All the blocks in the chain linked list must be destroyed

File(s): blockchain_destroy.c
Compiled: gcc -Wall -Wextra -Werror -pedantic -I. -o blockchain_destroy-test blockchain_destroy.c blockchain_create.c block_create.c block_destroy.c test/blockchain_destroy-main.c -L../../crypto -lhblk_crypto -lllist -lssl -lcrypto -pthread

✅ 4. Hash block

Write a function that computes the hash of a block

  • Prototype: uint8_t *block_hash(block_t const *block, uint8_t hash_buf[SHA256_DIGEST_LENGTH]);, where:
    • block points to the block to be hashed
  • The resulting hash must be stored in hash_buf
  • block->hash must be left unchanged.
  • Your function must return a pointer to hash_buf
  • You don’t have to allocate any memory dynamically

File(s): block_hash.c
Compiled: gcc -Wall -Wextra -Werror -pedantic -I. -o block_hash-test blockchain_create.c block_create.c block_destroy.c blockchain_destroy.c block_hash.c test/block_hash-main.c -L../../crypto -lhblk_crypto -lllist -lssl -lcrypto -pthread

✅ 5. Save blockchain

Write a function that serializes a blockchain into a file

  • Prototype: int blockchain_serialize(blockchain_t const *blockchain, char const *path);, where:
    • blockchain points to the blockchain to be serialized,
    • path contains the path to a file to serialize the blockchain into
  • If path points to an existing file, it must be overwritten
  • Your function must return 0 upon success, or -1 upon failure

Format

The resulting file should contain exactly the following:

File Header\

Offset Size (bytes) Field Purpose
0x00 4 hblk_magic Identifies the file as a valid serialized blockchain format. HBLK (48 42 4c 4b) in ASCII; these four bytes constitute the magic number.
0x04 3 hblk_version Identifies the version at which the blockchain has been serialized. The format is X.Y, where both X and Y are ASCII characters between 0 and 9.
0x07 1 blk_endian This byte is set to either 1 or 2 to signify little or big endianness, respectively. This affects interpretation of multi-byte fields.
0x08 4 hblk_blocks Number of blocks in the blockchain. Endianness dependent.
0x0C ? blocks List of blocks

Block\

The following table describes how a block is serialized. The blocks are serialized contiguously, the first one starting at offset 0x0C:

Offset Size (bytes) Field Purpose
0x00 4 index Block index in the blockchain. Endianness dependent.
0x04 4 difficulty Block difficulty. Endianness dependent.
0x08 8 timestamp Time at which the block was created (UNIX timestamp). Endianness dependent.
0x10 8 nonce Salt value used to alter the block hash. Endianness dependent.
0x18 32 prev_hash Hash of the previous block in the blockchain
0x38 4 data_len Block data size (in bytes). Endianness dependent.
0x3C data_len data Block data
0x3C + data_len 32 hash Block hash

File(s): blockchain_serialize.c
Compiled: gcc -Wall -Wextra -Werror -pedantic -I. -o blockchain_serialize-test blockchain_create.c block_create.c block_destroy.c blockchain_destroy.c block_hash.c blockchain_serialize.c provided/_endianness.c test/blockchain_serialize-main.c -L../../crypto -lhblk_crypto -lllist -lssl -lcrypto -pthread

✅ 6. Load blockchain

Write a function that deserializes a blockchain from a file

  • Prototype: blockchain_t *blockchain_deserialize(char const *path);, where:
    • path contains the path to a file to load the blockchain from
  • If the file pointed to by path doesn’t exist, or you don’t have the permission to open/read it, your function must fail
  • Your function must return a pointer to the deserialized blockchain upon success, or NULL upon failure
  • The format of the file to parse is described in the previous task
  • Upon any error, the function must fail and return NULL. Error cases:
    • Unable to open/read file
    • Incorrect magic number
    • Version mismatch

File(s): blockchain_deserialize.c
Compiled: gcc -Wall -Wextra -Werror -pedantic -I. -o blockchain_deserialize-test blockchain_create.c block_create.c block_destroy.c blockchain_destroy.c block_hash.c blockchain_deserialize.c provided/_blockchain_print.c provided/_endianness.c test/blockchain_deserialize-main.c -L../../crypto -lhblk_crypto -lllist -lssl -lcrypto -pthread

✅ 7. Block validity

Write a function that verifies that a block is valid

  • Prototype: int block_is_valid(block_t const *block, block_t const *prev_block);, where:
    • block points to the block to check
    • prev_block points to the previous block in the blockchain, or is NULL if block is the first block of the chain
  • The following requirements must be fulfilled for a block to be valid:
    • block should not be NULL
    • prev_block should be NULL ONLY if block‘s index is 0
    • If the block’s index is 0, the block should match the Genesis block described in the first task
    • The block’s index must be the previous block’s index, plus 1
    • The computed hash of the previous block must match the one it stores
    • The computed hash of the previous block must match the reference one stored in block
    • The computed hash of the block must match the one it stores
    • You don’t have to worry about the timestamp and the difficulty for this iteration of the blockchain.
    • The block data length must not exceed BLOCKCHAIN_DATA_MAX

File(s): block_is_valid.c
Compiled: gcc -Wall -Wextra -Werror -pedantic -I. -o block_is_valid-test blockchain_create.c block_create.c block_destroy.c blockchain_destroy.c block_hash.c block_is_valid.c test/block_is_valid-main.c -L../../crypto -lhblk_crypto -lllist -lssl -lcrypto -pthread

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