Maximum length for MD5 input/output

Question

What is the maximum length of the string that can have md5 hashed? Or: If it has no limit, and if so what will be the max length of the md5 output value?

Answer 1

MD5 processes an arbitrary-length message into a fixed-length output of 128 bits, typically represented as a sequence of 32 hexadecimal digits.

Answer 2

You can have any length, but of course, there can be a memory issue on the computer if the String input is too long. The output is always 32 characters.

Answer 3

There is no limit to the input of md5 that I know of. Some implementations require the entire input to be loaded into memory before passing it into the md5 function (i.e., the implementation acts on a block of memory, not on a stream), but this is not a limitation of the algorithm itself. The output is always 128 bits. Note that md5 is not an encryption algorithm, but a cryptographic hash. This means that you can use it to verify the integrity of a chunk of data, but you cannot reverse the hashing. Also note that md5 is considered broken, so you shouldn't use it for anything security-related (it's still fine to verify the integrity of downloaded files and such).

Answer 4

The algorithm has been designed to support arbitrary input length. I.e you can compute hashes of big files like ISO of a DVD...

If there is a limitation for the input it could come from the environment where the hash function is used. Let's say you want to compute a file and the environment has a MAX_FILE limit.

But the output string will be always the same: 32 hex chars (128 bits)!

Answer 5

• The length of the message is unlimited.

Append Length

A 64-bit representation of b (the length of the message before the padding bits were added) is appended to the result of the previous step. In the unlikely event that b is greater than 2^64, then only the low-order 64 bits of b are used.

• The hash is always 128 bits. If you encode it as a hexdecimal string you can encode 4 bits per character, giving 32 characters.
• MD5 is not encryption. You cannot in general "decrypt" an MD5 hash to get the original string.

See more here.

Answer 6

You may want to use SHA-1 instead of MD5, as MD5 is considered broken.

You can read more about MD5 vulnerabilities in this Wikipedia article.