 | MD5 File Comparison |  |
A Windows program to get the MD5 message digest of a file, | ||
| MD5 File Comparison | |
A Windows program to get the MD5 message digest of a file, | ||
The MD5 message digest of a file is a fixed-length hash value that uniquely represents the content of the file. "File" here means any sequence of characters or bytes, such as an article or an executable program. The "hash value" is a sequence of 32 letters and numbers which is derived from the file by a complicated algorithm, and which represents the contents of that file in such a way that any (even a very minor) change to that file results in a completely different hash value. This means it is possible to ascertain whether a copy of a file has been changed by comparing its hash value to the hash value of the original version of the file.
For example, consider a file A consisting of the ASCII characerts for "ant" and another file B consisting of the ASCII characters for "bat". Their MD5 message digests are:
| A | 63 B0 7E 82 8B F0 16 E9 76 FF 95 D6 EE 07 A1 05 | |
| B | 5F 3F 46 81 12 1B 46 0E 33 04 A1 88 7F 42 F1 C3 |
Here is a screenshot when two Excel file fin12.xls and fin13.xls are compared.
The Copy both button copies the two digital signatures to the clipboard:
| 7E 64 1D 67 74 E8 BD BD 66 EE 0D A7 07 8C 62 4B |
| 35 66 1A 7D 8B CC D2 FF A4 CF 23 75 C9 99 52 3C |
The primary use of this program is to verify the integrity of a file downloaded from the web (or available from some other sources, such as a CD-ROM or flash drive) — if the MD5 digital signature of the original file is known. If a file (e.g. a document or a program) is uploaded to the web then it can also be accompandied by its digital signature. If a copy of the file is available elsewere, then this program can be used to check whether the two copies are identical, and that nothing had been added to, or removed from, the original.