Abstract: Systems, devices, and methods are provided for stable pseudonymous identifiers. A system may obtain first data, and obtain a first cryptographic key from a cryptography service. The system may determine, based at least in part on the first data and the first cryptographic key, a first hash output of a hash function. The system may determine that a mapping table does not include a first record associated with the first hash output. The system may create, in the mapping table, a first record comprising the first hash output and a random value. The system may provide the random value as a stable pseudonymous identifier of the first data. If the first cryptographic key is subject to a key rotation, the pseudonymous identifier of the first data may remain constant even though the value of the key changes as a result of the key rotation.