Authentication is the act of proving an assertion, such as the identity of a computer system user. In contrast with identification, the act of indicating a person or thing's identity, authentication is the process of verifying that identity. It might involve validating personal identity documents, verifying the authenticity of a website with a digital certificate, determining the age of an artifact by carbon dating, or ensuring that a product or document is not counterfeit.
ATM user authenticating himself
A security hologram label on an electronics box for authentication
NSA KAL-55B Tactical Authentication System used by the U.S. military during the Vietnam War – National Cryptologic Museum
A military police officer checks a driver's identification card before allowing her to enter a military base.
To counterfeit means to imitate something authentic, with the intent to steal, destroy, or replace the original, for use in illegal transactions, or otherwise to deceive individuals into believing that the fake is of equal or greater value than the real thing. Counterfeit products are fakes or unauthorized replicas of the real product. Counterfeit products are often produced with the intent to take advantage of the superior value of the imitated product. The word counterfeit frequently describes both the forgeries of currency and documents as well as the imitations of items such as clothing, handbags, shoes, pharmaceuticals, automobile parts, unapproved aircraft parts, watches, electronics and electronic parts, software, works of art, toys, and movies.
Counterfeit t-shirts at a flea market.
Counterfeit Brazilian real banknotes
U.S. CBP Office of Field Operations agent checking the authenticity of a travel document at an international airport using a stereo microscope
Bulk bag of counterfeit Viagra