An integrated-circuit radio transmitter chip comprising: a radio transmitter; a cryptographic engine; and control logic for controlling the cryptographic engine, wherein the cryptographic engine is configured to perform a cryptographic operation by: receiving input data for the cryptographic operation; performing (42; 52) a first component process to generate first result data; performing (44; 54) a second component process to generate second result data; and using the first and second result data to generate output data representative of a result of the cryptographic operation; and outputting the output data, wherein the control logic comprises a radio-state input for determining (41, 43; 51, 53) whether the radio transmitter circuit is in an active state in which the radio transmitter circuit transmits one or more radio signals, and wherein the control logic is configured to use the radio-state input to: control the cryptographic engine to perform the first component process in response to determining that the radio transmitter circuit is in the active state, so that the radio transmitter circuit transmits a radio signal while the cryptographic engine performs the first component process; prevent the cryptographic engine from performing the second component process while the radio transmitter circuit is in the active state, such that the radio transmitter circuit does not transmit any radio signal while the cryptographic engine performs the second component process; and control the cryptographic engine to perform the second component process in response to determining that the radio transmitter circuit is not in the active state. a radio transmitter; a cryptographic engine; and control logic for controlling the cryptographic engine, receiving input data for the cryptographic operation; performing (42; 52) a first component process to generate first result data; performing (44; 54) a second component process to generate second result data; and using the first and second result data to generate output data representative of a result of the cryptographic operation; and outputting the output data, wherein the control logic comprises a radio-state input for determining (41, 43; 51, 53) whether the radio transmitter circuit is in an active state in which the radio transmitter circuit transmits one or more radio signals, and wherein the control logic is configured to use the radio-state input to: control the cryptographic engine to perform the first component process in response to determining that the radio transmitter circuit is in the active state, so that the radio transmitter circuit transmits a radio signal while the cryptographic engine performs the first component process; prevent the cryptographic engine from performing the second component process while the radio transmitter circuit is in the active state, such that the radio transmitter circuit does not transmit any radio signal while the cryptographic engine performs the second component process; and control the cryptographic engine to perform the second component process in response to determining that the radio transmitter circuit is not in the active state. control the cryptographic engine to perform the first component process in response to determining that the radio transmitter circuit is in the active state, so that the radio transmitter circuit transmits a radio signal while the cryptographic engine performs the first component process; prevent the cryptographic engine from performing the second component process while the radio transmitter circuit is in the active state, such that the radio transmitter circuit does not transmit any radio signal while the cryptographic engine performs the second component process; and control the cryptographic engine to perform the second component process in response to determining that the radio transmitter circuit is not in the active state.