ICSF provides callable services for developing SET applications that make use of the cryptographic hardware at the merchant and acquirer payment gateway. The SET Block Compose callable service performs DES encryption of data, OAEP-formatting through a series of SHA-1 hashing operations, and the RSA-encryption of the Optimal Asymmetric Encryption Padding (OAEP) block. The SET Block Decompose callable service decrypts both the RSA-encrypted and the DES-encrypted data.