1. A system comprising: a source device including: an interface configured to: receive an electronic document; transmit the electronic document to a dedicated signing device; and receive a signed electronic document from the dedicated signing device, the signed electronic document including the electronic document and an associated signature document including a digital image embedded with a digital watermark representing an encrypted one-way hash; memory configured to store a public key assigned to the dedicated signing device; a processor configured to: calculate a one-way hash of the electronic document; decode the digital watermark representing the encrypted one-way hash; decrypt the encrypted one-way hash using the stored public key assigned to the dedicated signing device; compare the decrypted one-way hash to the calculated one-way hash; and wherein the dedicated signing device includes: a signer interface configured to receive input from a signer; an external interface configured to: receive the electronic document from the source device; transmit the signed electronic document to the source device, the signed electronic document including the electronic document and the associated signature document; memory configured to store a private key assigned to the dedicated signing device; and a processor configured to: prevent alterations to the electronic document presented by the dedicated signing device; alter a characteristic of the signature document based on the signer input, the signature document comprising an arbitrary digital representation; calculate the one-way hash for the electronic document; encrypt the one-way hash using the stored private key assigned to the dedicated signing device; embed the digital watermark representing the encrypted one-way hash into the arbitrary digital representation, wherein the digital watermark is generated and embedded independent of any private key of the signer; and associating the electronic document with the altered signature document as the signed electronic document.
6. The system of claim 1 , wherein the one-way hash is a checksum.