Many objects in the XRP Ledger, particularly transactions and ledgers, are uniquely identified by a 256-bit hash value. This value is typically calculated as a "SHA-512Half", which calculates a [SHA-512](http://dx.doi.org/10.6028/NIST.FIPS.180-4) hash from some contents, then takes the first 64 characters of the hexadecimal representation. Since the hash of an object is derived from the contents in a way that is extremely unlikely to produce collisions, two objects with the same hash can be considered the same.

An XRP Ledger hash value has the following characteristics:

* Exactly 64 characters in length
* [Hexadecimal](https://en.wikipedia.org/wiki/Hexadecimal) character set: 0-9 and A-F.
* Typically written in upper case.

**Note:** SHA-512Half has similar security to the officially-defined _SHA-512/256_ hash function. However, the XRP Ledger's usage predates SHA-512/256 and is also easier to implement on top of an existing SHA-512 function. (As of this writing, SHA-512 support in cryptographic libraries is much more common than for SHA-512/256.)
