Authorising transactions in a mobile device

To authorise a transaction in a mobile device a wallet application 102 sends a PIN request and public key 107 to PIN entry application 106, which assumes control of the mobile device keypad to allow PIN entry and encrypts the entered PIN using public key 107 and a private key 111. The twice encrypted PIN is returned to wallet application 102 with trusted module certificate 112 containing trusted module public key 110 signed with an issuer private key (not shown). The twice encrypted PIN is then sent to payment application 104 with trusted module certificate 112 and a PIN verification request. Payment application 104 attempts to extract trusted module public key 110 from certificate 112 using its own copy of issuer public key 113 to determine whether the payment verification request is signed with the correct private key and thus from a trusted source. The successfully extracted trusted module public key 110 is then used to decrypt the PIN to further verify whether the PIN is encrypted with the trusted module private key 111, i.e. from a trusted source. The resulting data is then further decrypted using the payment application private key 108 to obtain the PIN data.