One embodiment provides a method, including: receiving, from a data owner, an input string of plaintext data comprising a plurality of characters for storage in a database of a third-party storage provider; arranging the plurality of characters of the input string as a half pyramid, wherein the half pyramid comprises a plurality of rows, each row comprising at least one more character than a preceding row; encrypting, using a secure encryption scheme and based upon a key, each row of the half pyramid independently from each other row of the half pyramid; and storing, in the database of the third-party storage provider, the encrypted rows of the half pyramid. Other aspects are claimed and described.