Understanding the Difference Between a Hex Decoded String and String.as_bytes() in Rust

Explore the fundamental differences between hex decoded strings and byte representations in Rust. Learn how these variations affect hashing and data encoding.
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The Problem at Hand

Imagine you have a string, such as "abcd12342020", and you want to hash it using the SHA-256 algorithm. You might think that hashing the string in its original form and its hex representation should yield similar results. However, as many developers quickly learn, this is not the case. Let's take a look at the Rust code that exemplifies this problem:

[[See Video to Reveal this Text or Code Snippet]]

In this case, h1 and h2 produce different hash outputs, leading us to question why this discrepancy occurs.

Breaking Down the Solution

To understand the difference in hashing results (h1 vs h2), we need to look closely at how each method processes the string.

1. Understanding .as_bytes()

The string "ab" is represented as:

[0x61, 0x62] (which corresponds to the ASCII values of 'a' and 'b').

This byte representation accurately reflects the binary data of the string, making it suitable for operations like hashing.

2. Understanding hex::decode()

On the other hand, the hex::decode() function interprets the string as a hexadecimal number. This means it reads pairs of characters and converts them into their byte equivalents. For instance:

The hex string "ab" is interpreted as:

0xAB (where 'a' = 10 and 'b' = 11 in hexadecimal).

So, when you apply hex::decode(&src), it treats the input string as a sequence of hexadecimal digits instead of plain text.

Key Takeaways

Hashing Divergence: This fundamental difference in how the string is processed leads to h1 and h2 ending up with different hash values.

Debugging with dbg!: If you're running into ambiguity, consider wrapping your variables with dbg! to inspect the differences directly.

Conclusion

Now that you have a clearer understanding, you can confidently use these methods in your Rust programming endeavors!