Signer Authentication Methods for E-Signatures
Every e-signature request answers one question before anyone types a name: is the person signing really who the other side thinks it is? The method you use to answer that is signer authentication, and it should scale with what the deal is worth.
Four ways to verify a signer, from light to heavy
Most e-signature tools offer a short menu of authentication methods. They differ in how much proof they demand from the signer and how much friction they add to a fast deal. For the trade, where a lot of agreements start as a verbal handshake, that trade-off is the whole decision. Picking well is less about security theater and more about matching effort to exposure.
Enforceability is the reason any of this matters. Under laws like the ESIGN Act and eIDAS, an electronic signature can be legally binding, but if a deal is ever disputed the burden falls on being able to show the signer was who they claimed to be. Authentication builds that proof into the transaction, and stronger methods support non-repudiation, the principle that a signer cannot later credibly deny having signed. The right level is the one that fits the risk in front of you, no higher.
Email or link access is the lightest option. The request goes to a specific address or phone number, and control of that inbox or message thread is the proof. If the link reached the person you already know and have traded with, opening it and typing a name is often enough. This is the default for low-risk, repeat-relationship deals, and it is the fastest path from agreement to signed PDF. It assumes the channel itself is trustworthy, which is usually fair when you chose the contact and have history with them.
SMS one-time code adds a second factor. The signer receives a numeric code by text and enters it on the signing page before the signature takes effect. It confirms the signer holds the phone number on file, which raises the bar against a forwarded link landing with the wrong person. The cost is one extra step and a dependency on cell coverage at the moment of signing, so it is best reserved for deals where confirming the device is worth a small delay.
Access code, sometimes called a shared secret, is a code you set and deliver through a separate channel, say a phone call or an in-person conversation. The signer types it to open the document. Because the code never travels with the link, it protects against an intercepted email, and it works when you want control over exactly who can open a draft. The weak point is coordination: both sides have to manage the code, and sending it in the same message as the link quietly defeats the purpose.
Knowledge-based authentication, or KBA, is the heaviest of the common four. The signer answers questions generated from public and commercial records, things only that individual should readily know. It is used when you have no prior relationship and the amount at stake justifies the friction. Signers sometimes fail legitimate attempts, so it suits high-value, first-time counterparties rather than everyday volume. For the rare deal where even KBA feels thin, document and ID verification sits one step beyond it, though that is a different weight class from the everyday menu.
Match the method to the deal, then read it off the record
Proportionality is the working rule. A repeat buyer you have shipped to a dozen times does not need KBA on a modest piece; forcing it just slows a deal that was never at risk. A first-time counterparty wiring a large sum for a watch you are shipping across a border is a different profile, and a stronger check is reasonable. The question to ask on each request is simple: if this deal went sideways, what would I wish I had required at signing? That one question sorts most deals faster than any checklist.
Deal value is the obvious input, but it is not the only one. Prior history with the signer, whether the goods ship before or after payment, the jurisdiction involved, and how the two sides first made contact all push the decision toward lighter or heavier verification. A good habit is to set a default for your typical deal and step up only when a specific factor warrants it, rather than treating every request as either trivial or high-stakes.
Whatever you choose, the method matters most after the fact, on the completion record. A defensible e-signature leaves an audit trail: who the request went to, when they opened it, the authentication step they cleared, the moment they signed, and the IP address tied to each action, all timestamped. That record, bound to the signed PDF and its reference number, is what turns a verbal "we have a deal" into something that holds up if the other side later disputes it.
The record is only useful if you can produce it when it counts, which is often months after signing. A signed PDF you can retrieve by reference number, with the full trail attached, is worth more in a dispute than a memory of how careful you were. Store the finished document where both sides can reach it, and treat the reference number as the thread back to everything that happened during signing.
When you review a finished document, confirm the authentication method you intended actually appears in the trail. An SMS code that was requested but skipped, or an access code that was emailed in the same thread as the link, weakens the record you are counting on. The point of choosing a method is defensibility, and defensibility lives in what the record can show, not in what you remember asking for. A quick scan before you close out the deal takes seconds and saves the argument you hope you never have.
For most dealers the practical answer is a tiered one. Keep the lightest workable method as your default so routine deals stay fast, keep a second factor ready for larger or unfamiliar counterparties, and make sure every signed PDF you keep carries a full, timestamped trail you can pull up later. That combination keeps speed where it belongs and adds proof where it counts. Lock the deal to the proof it deserves, no more and no less.