Techniques for preventing leakage of sensitive information through a signature are disclosed. Data is received, and the data is transmitted to a signature and encryption (SE) service, along with an encryption key. Signed and encrypted data is received from the SE service, where the signed and encrypted data is (i) encrypted using the encryption key and (ii) signed by the SE service. A verification is performed to verify that that sensitive information (such as the encryption key) is not leaked through a side channel of a signature of the signed and encrypted data, such as by (i) determining a length of the side channel of the signature, and (ii) verifying that the length of the side channel of the signature does not exceed a threshold length. Responsive to verifying that the sensitive information is not leaked through the side channel of the signature, the signed and encrypted data is transmitted.