# DSA

[Digital signatures video](https://www.youtube.com/watch?v=jbBe4AS5pk0\&index=18\&list=PL6N5qY2nvvJE8X75VkXglSrVhLv1tVcfy)

In order to understand *hex* and *type* parameters read [Hash](https://github.com/liesware/coherence/wiki/Hash)

### DSA

[spec](https://www.nist.gov/publications/digital-signature-standard-dss-2)

Description: Public-key cryptosystem

Problem: Discrete logarithm problem

Uses: Digital signatures

* It only supports "type":"string"

## How to ???

```python
import requests
import json
import os,binascii

def sending(message):
    url = 'http://127.0.0.1:6613/'
    response = requests.post(url, data=message)
    print response.content
    return response.content

def dsa(data_js, bits):
    req=json.loads(data_js)
    req["length"]=bits
    print "Send gen parameters : \n " + json.dumps(req) +"\n"
    data_js_n=sending(json.dumps(req))
    answ=json.loads(data_js_n)
    print "Recived  dsa gen: \n"+(json.dumps(answ)) +"\n\n\n"
    json_s=json_v='{ "version": 1 , "algorithm":"DSA", "type":"string","plaintext": "Hello world!", "hex":0,"privkey": "" ,"operation":"sign"}'
    req=json.loads(json_s)
    req["privkey"]=answ["privkey"]
    print "Send sign : \n " + json.dumps(req) +"\n"
    data_js_n=sending(json.dumps(req))
    answ_1=json.loads(data_js_n)
    print "Recived  sign done: \n"+(json.dumps(answ_1)) +"\n\n\n"
    json_v='{ "version": 1 , "algorithm":"DSA", "type":"string","plaintext": "Hello world!", "hex":0,"pubkey": "" ,"sign":"","operation":"verify"}'
    req=json.loads(json_v)
    req["pubkey"]=answ["pubkey"]
    req["sign"]=answ_1["sign"]
    print "Send verify : \n " + json.dumps(req) +"\n"
    data_js_n=sending(json.dumps(req))
    answ_2=json.loads(data_js_n)
    print "Recived  verify done: \n"+(json.dumps(answ_2)) +"\n\n\n"


dsa_gen='{ "version": 1 , "algorithm":"DSA", "operation":"gen", "length": 0 }'
dsa(dsa_gen,1024)
```

In this example we generate a DSA key (1024 bits), we sign *"Hello world!"* and validate it.

Json to generate

```javascript
{"operation": "gen", "version": 1, "length": INT, "algorithm": "DSA"}
```

* Length can be 1024, 2048 and 3072

Json to sign string

```javascript
{"algorithm": "DSA", "plaintext": "your string", "hex": BOOL, "version": 1, "operation": "sign", "type": "string", "privkey": "your private key"}
```

Json to validate string

```javascript
{"algorithm": "DSA", "plaintext": "Hello world", "pubkey": "your hex pubkey", "hex": 0, "sign": "your hex signature", "version": 1, "operation": "verify", "type": "string"}
```