USB Token is a hardware device. For security reasons Digital Signature Certificates must be stored into USB Tokens like Proxkey, Trustkey, e-Pass 2003 Auto, Safenet 5100, Aladdin, m-Token etc. There are many manufacturers who manufacture USB Tokens for Digital Signature Certificates. These USB Tokens are password protected.
As per CCA Guidelines issued on 7th December, 2013, Storage of Digital signature in FIPS Cryptographic USB Token is Mandatory
FIPS is Federal Information Processing Standards developed by US federal government for use in computer systems. FIPS is a standard for manudacturer to produce within guidelines. If product is being produced with FIPS Guidelines & found tested OK,product can be certified as FIPS Certified. As Digital Signature Certificate is very sensitive issue, hardware must be secured and certfied.