https://github.com/jmcph4/rfc1321
https://github.com/jmcph4/rfc1321
Last synced: about 1 year ago
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- Host: GitHub
- URL: https://github.com/jmcph4/rfc1321
- Owner: jmcph4
- License: other
- Created: 2024-12-15T04:25:09.000Z (over 1 year ago)
- Default Branch: master
- Last Pushed: 2025-01-11T08:56:24.000Z (over 1 year ago)
- Last Synced: 2025-04-04T06:31:15.821Z (over 1 year ago)
- Language: C
- Size: 10.7 KB
- Stars: 1
- Watchers: 1
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- Funding: .github/FUNDING.yml
- License: LICENSE
- Security: SECURITY.md
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README
# MD5 Reference Implementation in C as per RFC1321 #
The [MD5](https://en.wikipedia.org/wiki/MD5) cryptographic hash function is fully specified in [RFC 1321](https://www.ietf.org/rfc/rfc1321.txt)[1]. This document contains a reference implementation in the C programming language in its appendices (Appendix A, specifically). This repository contains what is largely a copy-paste of this implementation for both pedagogical and convenience purposes.
Quoting Appendix A directly:
> This appendix contains the following files taken from RSAREF: A
> Cryptographic Toolkit for Privacy-Enhanced Mail:
>
> global.h -- global header file
>
> md5.h -- header file for MD5
>
> md5c.c -- source code for MD5
>
> For more information on RSAREF, send email to .
>
> The appendix also includes the following file:
>
> mddriver.c -- test driver for MD2, MD4 and MD5
>
> The driver compiles for MD5 by default but can compile for MD2 or MD4
> if the symbol MD is defined on the C compiler command line as 2 or 4.
>
> The implementation is portable and should work on many different
> plaforms. However, it is not difficult to optimize the implementation
> on particular platforms, an exercise left to the reader. For example,
> on "little-endian" platforms where the lowest-addressed byte in a 32-
> bit word is the least significant and there are no alignment
> restrictions, the call to Decode in MD5Transform can be replaced with
> a typecast.
Any file within this repository that is not on this list is not part of the original RFC.
Additionally, Ronald Rivest's contact information is listed as:
> Ronald L. Rivest
>
> Massachusetts Institute of Technology
>
> Laboratory for Computer Science
>
> NE43-324
>
> 545 Technology Square
>
> Cambridge, MA 02139-1986
>
>
> Phone: (617) 253-5880
>
> EMail: rivest@theory.lcs.mit.edu
## Modifications ##
The original reference implementation in the RFC is intended for 32-bit machines. Due to the lack of standard integer types (a la `stdint.h`) at the time, `unsigned long int` was typecast to `UINT4` (and similarly for `UINT2`). When compiling on modern 64-bit machines these invariants of course break. As such, I have modified these type aliases accordingly. The Git-flavoured diff for this change is as follows:
```diff
diff --git a/global.h b/global.h
index 2ed41be..bc5029d 100644
--- a/global.h
+++ b/global.h
@@ -1,5 +1,6 @@
/* GLOBAL.H - RSAREF types and constants
*/
+#include
/* PROTOTYPES should be set to one if and only if the compiler supports
function argument prototyping.
@@ -14,10 +15,10 @@ The following makes PROTOTYPES default to 0 if it has not already
typedef unsigned char *POINTER;
/* UINT2 defines a two byte word */
-typedef unsigned short int UINT2;
+typedef uint16_t UINT2;
/* UINT4 defines a four byte word */
-typedef unsigned long int UINT4;
+typedef uint32_t UINT4;
/* PROTO_LIST is defined depending on how PROTOTYPES is defined above.
If using PROTOTYPES, then PROTO_LIST returns the list, otherwise it
```
## Security ##
As of the time of writing, MD5 has long been known to be cryptographically broken. Please consult RFC 6151[2] for technical guidance on its use.
## Bibliography ##
1. R. Rivest, "The MD5 Message-Digest Algorithm," RFC 1321, Internet Engineering Task Force (IETF), Apr. 1992. [Online]. Available: https://www.rfc-editor.org/rfc/rfc1321. [Accessed: Dec. 15, 2024].
2. L. Turner and S. Chen, "Updated Security Considerations for the MD5 Message-Digest and the HMAC-MD5 Algorithms," RFC 6151, Internet Engineering Task Force (IETF), Mar. 2011. [Online]. Available: https://www.rfc-editor.org/rfc/rfc6151. [Accessed: Dec. 15, 2024].