Digitally signing a document

1. An apparatus comprising:

a processor;

a memory that stores code executable by the processor to:

monitor for a trigger;

determine whether a digital document contains a user signature in response to the trigger;

apply a cryptographic digital signature to the digital document in response to the digital document including a user signature, wherein the cryptographic digital signature comprises information associated with the digital document that demonstrates the authenticity of the digital document;

detect one or more edits by a user associated with the user signature to the digital document after the cryptographic digital signature is applied to the digital document;

determine whether the one or more edits were made within a predetermined time period of application of the cryptographic digital signature;

determine, in response to determining that the one or more edits were made within a predetermined time period, whether the one or more edits satisfy at least one criterion comprising one of: an amount of editing, a type of edit, and a same application session;

automatically reapply the cryptographic digital signature to the digital document without requiring the user to apply a second user signature in response to determining that the one or more edits satisfy at least one criterion;

require the user making the one or more edits to apply a second user signature before reapplying the cryptographic digital signature to the digital document in response to the one or more edits not satisfying at least one criterion; and

require the user making the one or more edits to apply a second user signature before reapplying the cryptographic digital signature to the digital document in response to determining that the one or more edits were not made within a predetermined time period.

2. The apparatus of claim 1 , wherein the processor further generates a cryptographic digital signature for the digital document, wherein the cryptographic digital signature is generated based on the user signature.

3. The apparatus of claim 1 , wherein the processor further selects a cryptographic digital signature for the digital document, wherein the cryptographic digital signature is based on an identity of a signatory indicated by the user signature.

4. The apparatus of claim 1 , further comprising an electronic device that opens the digital document, wherein the cryptographic digital signature is based on an identity of the electronic device.

5. The apparatus of claim 1 , wherein the processor further verifies the user signature, wherein applying the cryptographic digital signature comprises applying the cryptographic digital signature in response to the user signature being a valid signature.

6. The apparatus of claim 5 , wherein verifying the user signature comprises:

accessing a user profile of an individual signing the document based on the user signature; and

checking whether the individual signing the document is authorized to sign the digital document based on the user profile.

7. The apparatus of claim 5 , wherein verifying the user signature comprises comparing the user signature to a plurality of valid user signatures.

8. The apparatus of claim 5 , further comprising a digitizer that receives the user signature, wherein verifying the user signature comprises comparing a handwriting characteristic of the user signature to a corresponding handwriting characteristic of a user identified by the user signature.

9. The apparatus of claim 1 , further comprising an imager that creates the digital document from a physical document, wherein the trigger comprises creation of the digital document.

10. A method comprising:

receiving a trigger;

determining, by use of a processor, whether a digital document contains a user credential in response to receiving the trigger;

applying a cryptographic digital signature to the digital document, the cryptographic digital signature based on the user credential, the cryptographic digital signature comprising information associated with the digital document that demonstrates the authenticity of the digital document;

detecting one or more edits by a user associated with the user signature to the digital document after the cryptographic digital signature is applied to the digital document;

determining whether the one or more edits were made within a predetermined time period of application of the cryptographic digital signature;

determining, in response to determining that the one or more edits were made within a predetermined time period, whether the one or more edits satisfy at least one criterion comprising one of: an amount of editing, a type of edit, and a same application session;

automatically reapplying the cryptographic digital signature to the digital document without requiring the user to apply a second user signature in response to determining that the one or more edits satisfy at least one criterion;

requiring the user making the one or more edits to apply a second user signature before reapplying the cryptographic digital signature to the digital document in response to the one or more edits not satisfying at least one criterion; and

requiring the user making the one or more edits to apply a second user signature before reapplying the cryptographic digital signature to the digital document in response to determining that the one or more edits were not made within a predetermined time period.

11. The method of claim 10 , further comprising creating a cryptographic digital signature using a private key associated with the user credential.

12. The method of claim 10 , further comprising selecting a cryptographic digital signature from a plurality of predefined cryptographic digital signatures based on the user credential.

13. The method of claim 10 , further comprising verifying the user credential, wherein applying the cryptographic digital signature comprises applying a cryptographic digital signature in response to the user credential being a valid signature.

14. The method of claim 10 , further comprising detecting a cryptographic digital signature for the digital document responsive to the trigger, and verifying that the user credential matches the detected cryptographic digital signature.

15. The method of claim 10 , wherein reapplying the cryptographic digital signature comprises generating a new cryptographic digital signature based on the edited digital document.

16. The method of claim 10 , wherein reapplying a cryptographic digital signature to the digital document without requiring the user to apply a second user signature in response to determining that the one or more edits satisfy at least one criterion comprises reapplying the cryptographic digital signature in response to the user correcting spelling within the digitally signed digital document, wherein reapplying the cryptographic digital signature comprises generating a new cryptographic digital signature based on the edited digital document.

17. The method of claim 10 , further comprising:

detecting an attempt to transfer the digitally signed document;

checking the validity of the cryptographic digital signature;

validating a sender in response to the cryptographic digital signature being out of date; and

reapplying the cryptographic digital signature to the digital document without requiring the user to apply a second user signature in response to validating the sender, wherein reapplying the cryptographic digital signature comprises generating a new cryptographic digital signature based on the sender.

18. The method of claim 10 , wherein the trigger comprises an action selected from the group comprising: saving the digital document, closing the digital document, and transferring the digital document.

19. A program product comprising a non-transitory computer readable storage medium that stores code executable by a processor, the executable code comprising code to perform:

detecting a trigger;

determining whether a digital document contains a user signature in response to the trigger;

verifying the user signature in response to the digital document including a user signature;

applying a cryptographic digital signature to the digital document, the cryptographic digital signature based on the user signature, wherein the cryptographic digital signature comprise information associated with the digital document that demonstrates the authenticity of the digital document;

detecting one or more edits by a user associated with the user signature to the digital document after the cryptographic digital signature is applied to the digital document;

determining whether the one or more edits were made within a predetermined time period of application of the cryptographic digital signature;

determining, in response to determining that the one or more edits were made within a predetermined time period, whether the one or more edits satisfy at least one criterion comprising one of: an amount of editing, a type of edit, and a same application session;

automatically reapplying the cryptographic digital signature to the digital document without requiring the user to apply a second user signature in response to determining that the one or more edits satisfy at least one criterion;

requiring the user making the one or more edits to apply a second user signature before reapplying the cryptographic digital signature to the digital document in response to the one or more edits not satisfying at least one criterion; and

requiring the user making the one or more edits to apply a second user signature before reapplying the cryptographic digital signature to the digital document in response to determining that the one or more edits were not made within a predetermined time period.

20. The program product of claim 19 , wherein reapplying the cryptographic digital signature to the digital document without requiring the user to apply a second user signature in response to determining that the one or more edits satisfy at least one criterion comprises generating a new cryptographic digital signature based on the edited digital document in response to the user editing the digital document before closing the digital document.