Cryptographic signatures

[mantycore]

• [x] A browser node will generate a private key (probably in a style of xkcd password, for ease of human use)
• [x] Each post will be signed by the key with zk signature
• [x] A possible vulnerability: using the same key to sign the exact same text will result in the same signature; an unique post id included in the signed object solves this
• [x] In event when user wants to identify as an author of a post (e.g. for revoking it, issuing a modified version, moderating a thread started with the post), they will sign the command with zk mark using the private key and the original post.
• [x] The private key may be stored in localStorage and may be transfered to another browser by copying and pasting.

[mantycore]

Reimplemented zk-proof-mark using big-integer; found a bug caused by negative exponent. Need to adjust bit lengths of values used.

[mantycore]

Decided against using ad-hoc implementation, instead will use inverted asymmetric cryptography scheme.

[mantycore]

Invert asymmetric cryptography is also ill advised, instead implemented the original scheme using NaCl signatures with the key pair generated from the message hash instead of Schnorr algorithm.