Mobile devices as security tokens

A method useful in authenticating a transaction with a target system, through use of a computer system and a portable system, the method including:

• sharing state information between the portable system and the computer system across a network;
• the portable system encoding image data with a digital watermark that conveys a payload, the payload being based, at least in part, on the shared state information;
• presenting the digitally watermarked image for sensing by the target system, so that the payload data can be recovered from the sensed image and used by said computer system to authenticate a transaction with the target system;
• wherein the portable system is employed in authenticating a transaction with the target system, through use of network communication of state information, and optical communication of visual information.

A method useful in authenticating a transaction with a target system, through use of a computer system and a portable system, the method including:

• the target system sensing visual data presented by the portable system, the portable system having earlier produced a single-use image for presentation through use of secret information shared between the computer system and the portable system;
• processing visual information that corresponds to the sensed visual data, in conjunction with the secret information, to produce authentication data;
• and
• receiving authorization information from the computer system at the target system, across a network, based on said authorization data;
• wherein authentication of a transaction with the target system involves one-way optical communication of visual information to the target system from a portable system, and two-way network communication of information between the target system and the computer system.

A method useful in authenticating a transaction with a target system, through use of a computer system and a portable system, the method including:

• the target system receiving information from the computer system across a network;
• the target system presenting a single-use image, based on the received information, for sensing by the portable system, so that the portable system can process the sensed image with secret data earlier shared between the computer system and the portable system, and produce authentication data based on the sensed image and the secret data, which authentication data is sent to the computer system;
• and
• the target system receiving authorization information from the computer system, across a network, based on the authorization data sent to the computer system;
• wherein authentication of a transaction with the target system involves optical communication of visual information to the portable system from the target system.

A method useful in authenticating a transaction with a target system, through use of a computer system and a portable system, the method including:

• the computer system and the portable system sharing secret information across a network;
• the computer system providing information to the target system across a network, the provided information enabling the target system to produce a single-use image for presentation by the target system and for optical sensing by the portable system;
• the computer system receiving authentication data from the portable system, the portable system having produced the authentication data based on both the shared secret information and the single-use image sensed from the portable system;
• and
• the computer system transmitting authorization information to the target system across the network, based on the authentication data received from the portable system;
• wherein authentication of a transaction with the target system involves one-way optical communication of visual information between the target system and the portable system, and two-way network communication of information between the target system and the computer system.

A method useful in authenticating a transaction with a target system, through use of a computer system and a portable system, the method including:

• the computer system and the portable system sharing secret information across a network, so that the portable system can present a one-time image based thereon;
• the computer system receiving information from the target system across a network, the received information corresponding to the one-time image presented by the portable system and sensed by the target system;
• and
• the computer system transmitting authorization information to the target system across the network, based on the received information;
• wherein authentication of a transaction with the target system involves one-way optical communication of visual information between the target system and the portable system, and two-way network communication of information between the target system and the computer system.

A portable system with which state information has been shared by a remote system, the portable system including a camera, the system being configured to:

• decode a digital watermark payload from imagery captured by the camera;
• apply a mapping function to the state information and the decoded digital watermark payload to yield an authentication key;
• and
• transmit the authentication key to the remote system, so as to authorize a further transaction by the portable system or a user thereof.