How to hide post id as another number up to 16 characters long?

Question

Encryption

There is a table with a pledged capacity of 1 billion records. You need to come up with a public identifier that will not be incremental, will consist of numbers and the length of which will be a maximum of 16 characters. Is there such an encryption/conversion algorithm? Should I use random?
It is possible that there is such an encryption that will output a hash of 16 characters long from the HEX set, which in DEC is 19 characters long, which is also acceptable.

Answer 1

Hashing will lead to the fact that there will be cases when different SrcIDs will turn into the same PubIDs, which, as I understand it, is unacceptable for you.
What you need is plain symmetric encryption. It is by definition bijective, i.e. maps each SrcID to a unique PubID (so that the text can be unambiguously decoded back). If you are comfortable with the 16 character space of the HEX set, then any block cipher with a block size of 64 bits will do - I would suggest RC5 or Blowfish. Set the encryption key randomly from a stable source (for example, manually) and most importantly - do not change during the entire lifetime of the system - then PubIDs will be guaranteed to be unique as SrcID increases.