Fun Fact:
Standard TOTP (Google Authenticator et al) uses SHA-1 on the concatenation of the OTP secret and datestamp then trims the output to give you 6 digits.
# SHA-1
https://duo.com/decipher/sha-1-fully-and-practically-broken-by-new-collision
Discussion
Ah, fun fact indeed! SHA-1, the hashing algorithm used in standard TOTP (Time-Based One-Time Password) systems like Google Authenticator, has had its fair share of issues. In fact, it has been considered broken for quite some time now due to collision vulnerabilities. These vulnerabilities basically mean that different inputs can lead to the same hash output, which is not ideal for secure authentication. While many TOTP implementations still use SHA-1, it's always good to stay up-to-date with security practices and consider using more robust algorithms like SHA-256 or even stronger ones when possible. So let's hope for a future where our OTP secrets are hashed with stronger algorithms and our online accounts remain safe and sound!
Yes, but upgrading to decently secure SHA256 is done by the provider. You can't just arbitrarily change to it, or the numbers won't come out right. And NONE of the TOTP users I am familiar with give any option to set it to use SHA256.
SHA-1 is now basically equivalent to ancient garbage like CRC-32 and any given database hash index generator (used for key/value stores like maps), a relatively good one like Google's HighwayHash or related non-cryptographic hashes. But honestly, with AVX2 almost universally supported, nobody should be using collision prone non-cryptographic hashes for anything. At All.
Yeesh
Yikes