Machine-readable symbols

A copy-resistant symbol comprising:

• a substrate;
• and
• a machine-readable symbol instantiated on the substrate,
• wherein:
• the machine-readable symbol represents a combination of substantive information and encrypted security information;
• and
• a decryption of the encrypted security information identifies a security feature of the copy-resistant symbol identifiable through optical imaging of the copy-resistant symbol.

A method of reading a copy-resistant symbol having a substrate and a machine-readable symbol instantiated on the substrate, the method comprising:

• optically acquiring the machine-readable symbol from the copy-resistant symbol;
• decoding the machine-readable symbol to derive a message;
• decrypting a portion of the message by applying a decryption key to the portion of the message;
• determining a security feature from the decrypted portion of the message;
• and
• confirming a physical presence of the security feature on the copy-resistant symbol.

An optical reader comprising:

• an illumination source disposed to illuminate a presented copy-resistant symbol;
• a detection device disposed to receive light scattered from the presented copy-resistant symbol;
• and
• a computational unit interfaced with the detection device and having:
• instructions to optically acquire a machine-readable symbol from the presented copy-resistant symbol;
• instructions to decode the machine-readable symbol to derive a message;
• instructions to decrypt a portion of the message by applying a decryption key to the portion of the message;
• instructions to determine a security feature from the decrypted portion of the message;
• and
• instructions to optically confirm a physical a presence of the security feature on the presented copy-resistant symbol with the detection device.