| | 1 | Each place a hash function is used within Tahoe, the data to be hashed is first prepended with a distinct "tag", one per purpose. |
| | 2 | |
| | 3 | These tags are encoded as a NetString, to insure that they cannot be confused with the data being hashed. For example, the VerifierId is computed as the SHA-256 hash of the following string: |
| | 4 | {{{ |
| | 5 | "23:allmydata_verifierid_v1," + DATA |
| | 6 | }}} |
| | 7 | |
| | 8 | This technique is especially important to distinguish the leaf nodes from the internal nodes in a MerkleHashTree, because otherwise an attacker can trivially construct leaf data that results in the same root hash as a previously constructed tree. |
