“To provide for the punishment of counterfeiting the securities and current coin of the United States;” Article 1, Section 8, Clause 6, US Constitution.
The definition of counterfeit according to the online legal dictionary is:
“The process of fraudulently manufacturing, altering, or distributing a product that is of lesser value than the genuine product.”
Through the years, there have been question as to why this power is enumerated in Section 8, Clause 6 of the US Constitution.
This duty would be covered under the “Necessary and Proper Clause”, which states,
”The Congress shall have Power To …make all Laws which shall be necessary and proper for carrying into Execution the foregoing Powers, and all other Powers vested by this Constitution in the Government of the United States, or in any Department or Officer thereof.”
This is Article 1, Section 8, Clause 18, which I will discuss in a later post. This clause allows Congress to adjust to the changing needs of the nation. It is also called the elastic clause, because it can be interpreted in a flexible manner. The punishment of counterfeiting would naturally flow from the powers to borrow money and regulate coinage according to Justice Joseph Story in his Commentaries on the Constitution of the United States.
The reason that the Constitutional Convention singled out this particular crime was to prevent the use of Bills of Attainder (to be discussed in a future post); to specifically cover the topic of foreign securities, and to make sure this was controlled by the Federal government and not the States; and to again emphasize that the Federal government controlled domestic money exchange issues, and not the States.
The law is currently interpreted to allow the Federal government to punish the act of making counterfeit money, but the States now punish the uttering or passing of counterfeit currency.
We the people give Congress the power to punish people who make counterfeit money or false government bonds or false foreign securities.
The benefit to we the people is that we have a government service that safeguards the value of money and securities.
The United States Secret Service is responsible for overseeing counterfeit information. Here is a link to an article on how to identify counterfeit currency: http://www.secretservice.gov/money_detect.shtml
References:
Findlay, Bruce Allyn and Findlay, Esther Blair. Your Rugged Constitution. Stanford: Stanford University Press, 1950
US Constitution
Online legal dictionary
Reclaiming the Shining City 
I learn something new every time you post a blog. Thanks