Not encryption but hashing
...the pesky old SHA-1 encryption algorithm...
The SHA-1 algorithm has no encryption properties whatsoever. It cannot encrypt or decrypt anything at all.
The SHA-1 algorithm is a hashing algorithm used to identify a message or block of data in a unique way but using only a small string of numbers, or hash value.
However, as noted, the old algorithm cannot uniquely identify messages or data because collisions have been found (same hash value for different input). You can no longer use the hash value for identification/integrity purposes once collisions are known to happen and the algorithm must be retired.