Various examples are provided related to a block cipher adaptation of the Galois Extension Fields (GEF) combination technique. In one example, a GEF-based block encryption includes forming an output from a PRNG into a key matrix, where the key matrix is formatted as an invertible square matrix; applying a GEF operation to the key matrix to map elements to a closed subset in a higher-order GEF space; mapping plaintext to a plaintext matrix; applying a GEF operation to the plaintext matrix to map elements to the higher-order GEF space; combining the plaintext matrix and the key matrix to produce a vector of ciphertext in the higher-order GEF space; reducing the vector to a reduced vector of ciphertext using an inverse of the GEF operation; and during the reducing, applying a ceiling operation to bijectively map elements in the reduced vector to a closed subset. Another example includes GEF-based block decryption.