6. The method of claim 1 , further comprising: by the mobile electronic device, receiving a request to access the encrypted document; determining whether the request is accompanied by a valid decryption action; and if the request includes a valid decryption action, then decrypting the encrypted document and presenting a decrypted version of the encrypted document to a user of the mobile electronic device, otherwise neither decrypting the encrypted document nor presenting the decrypted version of the encrypted document to the user.
7. The method of claim 6 , wherein determining whether the request is accompanied by a valid decryption action comprises, by the mobile electronic device: detecting that a computational tag having decryption capability is in proximity to the mobile electronic device; transmitting an encrypted object to the computational tag, wherein the encrypted object comprises the encrypted document or the encrypted key; and receiving a decrypted version of the encrypted object from the computational tag.