How to Use the Command 'rhash' (with examples)

Rhash is a robust command-line utility designed for calculating and checking various message digests. It’s particularly beneficial for verifying file integrity and ensuring that the data remains unchanged during transfer or storage. The tool supports a wide range of hashing algorithms, making it a versatile choice for many types of cryptographic needs.

Use case 1: Calculate default CRC32 digests of a file

Code:

rhash path/to/file

Motivation:

When you need to ensure the integrity of a file, calculating its CRC32 digest is a quick way to check if the file has been altered. CRC32 is mainly used in network and file integrity verification, providing a checksum to confirm the data’s correctness without going through a computationally expensive hashing process.

Explanation:

• rhash: Invokes the rhash utility to perform hashing operations.
• path/to/file: Specifies the path to the file for which you want to calculate the CRC32 digest.

Example Output:

a1b2c3d4  /path/to/file

Use case 2: Recursively process a directory to generate an SFV file using SHA1

Code:

rhash --sha1 --recursive path/to/folder > path/to/output.sfv

Motivation:

Generating an SFV file with SHA1 checksums for a directory of files is extremely useful when you plan to share or archive files. By saving the checksums in an SFV file, you can later verify the integrity of these files to ensure no corruption has occurred over time or during transmission.

Explanation:

• --sha1: Specifies that SHA1 algorithm should be used for generating checksums.
• --recursive: Tells rhash to process all files within the specified directory recursively.
• path/to/folder: Designates the directory that contains the files for which SHA1 checksums are to be created.
• > path/to/output.sfv: Redirects the output of the command to a file named output.sfv which will hold all SHA1 checksums.

Example Output:

6bcd50fe6eaa3450c12779145180d2b8374f3650 *path/to/folder/file1.txt
d9d107feee8bcb4f10cde3c1a07cf20db29e9482 *path/to/folder/file2.doc

Use case 3: Verify the integrity of files based on an SFV file

Code:

rhash --check path/to/file.sfv

Motivation:

Once you have an SFV file with stored checksums, you can verify that the files within your directory match the checksums listed. This is crucial in situations where files must remain untouched after being sent to another party or when retrieved from storage.

Explanation:

• --check: Directs rhash to perform a verification operation, comparing calculated checksums against those in an SFV file.
• path/to/file.sfv: Points to the SFV file containing the expected hashes for verification.

Example Output:

Everything OK

Use case 4: Calculate the SHA3 digest of a text message

Code:

rhash --sha3-256 --message 'message'

Motivation:

Hashing text messages or strings is a common practice in software development, particularly for password hashing and data validation. SHA3-256 is a member of the SHA-3 family, offering a high level of security for cryptographic purposes.

Explanation:

• --sha3-256: Directs rhash to use the SHA3-256 algorithm for hashing.
• --message: Indicates that the input is a string message rather than a file.
• 'message': The text message you want to hash.

Example Output:

e617ae17b29666da3d6344348766549f0b407e895fcf16dc97d99e11227ddcb6

Use case 5: Calculate CRC32 digest of a file and output digest encoded in base64 using BSD format

Code:

rhash --base64 --bsd path/to/file

Motivation:

Encoding digests in base64 is practical when you need a compact, textual representation of a hash that can be easily shared or logged. Using the BSD format allows for a standardized checksum signature that is widely recognized.

Explanation:

• --base64: Instructs rhash to encode the checksum output in base64 format.
• --bsd: Outputs the checksum in BSD format, typically used for distribution and verification purposes.
• path/to/file: The file whose CRC32 checksum is desired.

Example Output:

CKSUM (file) = W1Pdmg0=

Use case 6: Use custom output template

Code:

rhash --printf '%p\t%s\t%{mtime}\t%m\n' path/to/file

Motivation:

When integrating rhash with other data processing systems or logging the results, a custom template allows users to format the output according to their specific needs, ensuring that all necessary information is captured.

Explanation:

• --printf '%p\t%s\t%{mtime}\t%m\n': Indicates a custom output template where:
  • %p represents the file path,
  • %s indicates the file size,
  • %{mtime} outputs the file’s last modification time,
  • %m provides the message digest, followed by a newline character \n.
• path/to/file: The file to be processed with this custom output template.

Example Output:

path/to/file	1024	1609459200	a1b2c3d4

Conclusion:

Rhash is a versatile and powerful tool for calculating and verifying hashes. It supports a variety of use cases, from ensuring file integrity to processing directories and customizing digest outputs. Whether you’re a developer, network administrator, or data analyst, understanding the nuances of tools like rhash can significantly enhance your ability to manage file integrity and data security.