A method of communicating with at least one detonator assembly which is selected from a plurality of detonator assemblies in a blasting system which includes a control unit which is connected, directly or by using wireless techniques, to a loop which surrounds a plurality of boreholes each of which contains a wireless detonator assembly, the method including the steps of: 1) providing a plurality of encryption keys, each encryption key being uniquely associated with a selected detonator assembly, or a selected group of detonator assemblies, in the plurality of detonator assemblies; 2) storing each encryption key in the selected detonator assembly, or in the selected group of detonator assemblies, with which the encryption key is uniquely associated; 3) storing at least one of said encryption keys in a memory unit associated with the control unit; 4) at the control unit encrypting a message to form an encrypted message intended only for a selected detonator assembly, or for a selected group of detonator assemblies, using the respective encryption key which is uniquely associated with the selected detonator assembly or the selected group of detonator assemblies; 5) transmitting the encrypted message to the plurality of detonator assemblies by modulating a magnetic signal which is established by energising the loop; 6) receiving said encrypted message at each detonator assembly; 7) at each detonator assembly undertaking a decryption process on the received message using the encryption key which is uniquely associated with the detonator assembly to produce a decrypted message; 8) validating the decrypted message; and 9) after a successful validation process, further processing the decrypted message; characterised in that, in step 4, the message and appended validation code are encrypted to produce the encrypted message and in that at each detonator assembly, at which the decryption process is carried out, a validation code is calculated from the decrypted message and this is compared to the validation code and if the validation codes (52/34) match the decrypted message is further processed in a step. 1) providing a plurality of encryption keys, each encryption key being uniquely associated with a selected detonator assembly, or a selected group of detonator assemblies, in the plurality of detonator assemblies; 2) storing each encryption key in the selected detonator assembly, or in the selected group of detonator assemblies, with which the encryption key is uniquely associated; 3) storing at least one of said encryption keys in a memory unit associated with the control unit; 4) at the control unit encrypting a message to form an encrypted message intended only for a selected detonator assembly, or for a selected group of detonator assemblies, using the respective encryption key which is uniquely associated with the selected detonator assembly or the selected group of detonator assemblies; 5) transmitting the encrypted message to the plurality of detonator assemblies by modulating a magnetic signal which is established by energising the loop; 6) receiving said encrypted message at each detonator assembly; 7) at each detonator assembly undertaking a decryption process on the received message using the encryption key which is uniquely associated with the detonator assembly to produce a decrypted message; 8) validating the decrypted message; and 9) after a successful validation process, further processing the decrypted message;