Multisignature Bitcoin addresses require more than one key to authorize a transaction. In the case of Sig3, at least two keys must verify the transaction. This may be the user and Sig3, or multiple users or user keys.
Through Sig3, users select conditional policies which must be met before a transaction is approved. Example rules include auto-approving by date, transaction size, white-listed addresses, recipient address(es), or text message (SMS) verification. If a transaction does not meet policy requirements, Sig3 notifies the user of the violation via email or SMS.
Sig3 is currently integrated with Copay, BitPay‘s open-source multisig wallet platform. Reddit user “DisruptorNation,” a spokesperson for Sig3, wrote, “Beyond Copay we’ll [be] working on integrating with Electrum and Coinkite as the next step.” Electrum is an open-source Bitcoin wallet with support for Android, Linux, Windows, and Mac OSX. Coinkite is an online multisig wallet platform with additional merchant tools.
For developers looking to integrate Sig3 into their own applications, the Sig3 site explains that development of an API is underway.
While speaking about the goals of the project and multisig technology, the Sig3 team says on their site,
“The technology is extremely important and should be adopted by all exchanges and wallets, but it also introduces a level of complexity that many people aren’t familiar with. This complexity stands in the way of mass adoption. Sig3’s goal is to make transacting with bitcoin as easy as it used to be, but with the security of the future.”