While the security of the hash itself can be a concern, the technique is always valuable:
1. In particular, the domain of email addresses is less vulnerable to rainbow tables than the domain of phone numbers.
2. Using salts and a slow hash function improves security by requiring custom rainbow tables that take longer to build.
3. In a B2C situation, an easy appeal to justice can be made that a business should not be making a concerted effort to break its own customer privacy protection. This would not look good in court.
4. If additional consumer protection laws are needed, one-way hashing for the purpose of privacy could be considered a form of pro-consumer DRM. In that realm we have precedents for anti-circumvention laws and contracts.
1. In particular, the domain of email addresses is less vulnerable to rainbow tables than the domain of phone numbers.
2. Using salts and a slow hash function improves security by requiring custom rainbow tables that take longer to build.
3. In a B2C situation, an easy appeal to justice can be made that a business should not be making a concerted effort to break its own customer privacy protection. This would not look good in court.
4. If additional consumer protection laws are needed, one-way hashing for the purpose of privacy could be considered a form of pro-consumer DRM. In that realm we have precedents for anti-circumvention laws and contracts.