Understanding the 'b3sum' Command (with examples)

The b3sum command is a powerful tool used to calculate BLAKE3 cryptographic checksums for files and streams of data. BLAKE3 is a modern cryptographic hash function that is known for its speed, security, and ease of use. With b3sum, users can verify the integrity of their files, ensuring that they have not been tampered with or corrupted during transfers or storage. This command serves various use cases, from simple file integrity checks to more complex batch verification tasks.

Use case 1: Calculate the BLAKE3 checksum for one or more files

Code:

b3sum path/to/file1 path/to/file2 ...

Motivation:

Using b3sum to calculate the BLAKE3 checksums for files is essential for verifying data integrity. When files are transferred between locations or stored for long periods, they can become corrupted. Checksums are a reliable way to detect such corruptions by allowing a comparison between the current checksum and a previously calculated one.

Explanation:

• b3sum: The command-line tool that computes the BLAKE3 checksum.
• path/to/file1 path/to/file2 ...: Specifies the paths of the files for which you want to calculate the checksums. This can be one or multiple files.

Example Output:

b3fb0a75efdd1ec7b689502748cef2d19d8abcda76ec1423b8f8ea3c46441e97  path/to/file1
5b1f2d5ae1692037e24f4f28d9a0b6dfda3b59e77e202d4337e733dc4dfdce83  path/to/file2

Use case 2: Calculate and save the list of BLAKE3 checksums to a file

Code:

b3sum path/to/file1 path/to/file2 ... > path/to/file.b3

Motivation:

Saving the list of checksums to a file can be useful for batch verification later on. By storing these checksums, you establish a reference point against which you can verify the integrity of files at a future time, enhancing data reliability and security.

Explanation:

• b3sum: Computes the BLAKE3 checksums.
• path/to/file1 path/to/file2 ...: Specifies the files for checksum calculation.
• >: Redirects the output (checksums and filenames) from the terminal to a file.
• path/to/file.b3: The file where calculated checksums are saved. This text file will contain each file’s checksum and path.

Example Output:

(The content of path/to/file.b3)

b3fb0a75efdd1ec7b689502748cef2d19d8abcda76ec1423b8f8ea3c46441e97  path/to/file1
5b1f2d5ae1692037e24f4f28d9a0b6dfda3b59e77e202d4337e733dc4dfdce83  path/to/file2

Use case 3: Calculate a BLAKE3 checksum from stdin

Code:

command | b3sum

Motivation:

Calculating a checksum from stdin is beneficial in scenarios where data is being processed in a pipeline. This is common in environments where data is dynamically generated or transformed and you need to verify the integrity of this stream without saving it as a file first.

Explanation:

• command: Represents any command that outputs data you wish to checksum.
• |: Pipes the output of the preceding command into b3sum.
• b3sum: Calculates the BLAKE3 checksum of the piped data.

Example Output:

09160d72a028fbf8cfa474d964f972f141b015ad46c9b43b78409c1b0bfcf228  -

(The - indicates that the input was from stdin.)

Use case 4: Read a file of BLAKE3 checksums and filenames and verify all files have matching checksums

Code:

b3sum --check path/to/file.b3

Motivation:

This use case is critical for situations where you need to verify the integrity of multiple files against their previously stored checksums. It ensures that files have not changed since the checksums were computed, which is particularly useful for maintaining data consistency in backups or deployments.

Explanation:

• b3sum: Executes the checksum verification.
• --check: An option that tells b3sum to check each file against its recorded checksum.
• path/to/file.b3: The file containing the stored checksums that b3sum will use to verify the corresponding files.

Example Output:

path/to/file1: OK
path/to/file2: OK

Use case 5: Only show a message for missing files or when verification fails

Code:

b3sum --check --quiet path/to/file.b3

Motivation:

This example is handy when you need concise output, especially when working with large batches of files. By suppressing successful checks, it helps focus attention on files that are either missing or have failed their integrity checks, speeding up troubleshooting.

Explanation:

• b3sum: Executes the command.
• --check: Instructs b3sum to verify the files against stored checksums.
• --quiet: Suppresses normal output, displaying messages only in the event of missing files or failed verifications.
• path/to/file.b3: The checksum file used for verification.

Example Output:

path/to/file2: FAILED

Use case 6: Check a known BLAKE3 checksum of a file

Code:

echo known_blake3_checksum_of_the_file path/to/file | b3sum --check

Motivation:

Verifying a known checksum provides certainty that a specific file has not been altered from a known good state. This is crucial in environments requiring strict data integrity assurance, such as software development, scientific research, and digital forensics.

Explanation:

• echo: Outputs the known checksum followed by the file path.
• known_blake3_checksum_of_the_file: The checksum you expect the file to match.
• path/to/file: The file you are verifying.
• |: Pipes the echoed data into b3sum.
• b3sum --check: Compares the provided checksum against the actual checksum of the specified file.

Example Output:

path/to/file: OK

Conclusion:

The b3sum command is a versatile and robust utility for managing file integrity through BLAKE3 checksum calculations and verifications. Its application spans multiple scenarios from single file checks to handling batches of files efficiently, making it an invaluable tool for data integrity assurance across several domains.