I have been studying a Supreme Court case "IMS Health vs Sorrel".
In this case a Friend of Court brief filled by "Electronic Privacy Information Center" states that use of MD5 hash function to link multiple records together is suspect, since MD5 is broken.
I find this argument incorrect, the only use of MD5 (it is unknown whether it is salted or not) is to compute a hash to protect patient identity and not for signing purpose. Thus the usual arguments against use of MD5 do not apply.
Here is the quote from the brief http://epic.org/amicus/sorrell/EPIC_amicus_Sorrell_final.pdf
The first is the deidentification of the patient’s actual identity through a cryptographic technique known as “hashing.”
In ideal circumstances, a record containing the hashed representation of the patient’s actual identity could never be linked to the actual patient. But the cryptographic technique chosen to protect patient privacy in this matter has been suspect for at least 15 years, can now be broken using nothing more than an ordinary desktop computer, and is considered unsuitable for further use by the federal government.
Vlastimil Klima, Finding MD5 Collisions – A Toy For a Notebook (Mar. 5, 2005);9 Chad Dougherty, Vulnerability Note VU#836068: MD5 Vulnerable to Collision Attacks, United States Computer Emergency Readiness Team (Dec. 31, 2008).10 See generally, Wikipedia, “MD5,” (“. . .
it has been shown that MD5 is not collision resistant; as such, MD5 is not suitable for applications like SSL certificates or digital signatures that rely on this property. . . . The security of the MD5 hash function is severely compromised.”)11