# ECDH

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

### ECDH

[spec](https://csrc.nist.gov/publications/detail/sp/800-56a/rev-2/final)

Description: Public-key cryptosystem

Problem: Discrete logarithm problem

Uses: Key exchange

## 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 ecdh(data_js):
    req=json.loads(data_js)
    curve=req["curve"]
    print "Send gen parameters (A): \n " + json.dumps(req) +"\n"
    data_js_n=sending(json.dumps(req))
    answ=json.loads(data_js_n)
    print "Recived gen parameters donde (A): \n" + (json.dumps(answ)) +"\n\n\n"
    data_js_n=sending(json.dumps(req))
    print "Send gen parameters (B): \n " + json.dumps(req) +"\n"
    answ_1=json.loads(data_js_n)
    print "Recived gen parameters donde (B): \n" + (json.dumps(answ_1)) +"\n\n\n"
    gen='{ "version":1 , "algorithm":"ECDH","family": "", "privkey":"","sharedpub":"", "operation":"agree"}'
    req=json.loads(gen)
    req["privkey"]=answ["privkey"]
    req["sharedpub"]=answ_1["pubkey"]
    req["curve"]=curve
    print "Send agreetment (A): \n " + json.dumps(req) +"\n"
    data_js_n=sending(json.dumps(req))
    answ_2=json.loads(data_js_n)
    print "Recived agreetment donde (A): \n" + (json.dumps(answ_2)) +"\n\n\n"
    req["privkey"]=answ_1["privkey"]
    req["sharedpub"]=answ["pubkey"]
    print "Send agreetment (B): \n " + json.dumps(req) +"\n"
    data_js_n=sending(json.dumps(req))
    answ_3=json.loads(data_js_n)
    print "Recived agreetment donde (B): \n" + (json.dumps(answ_3)) +"\n\n\n"


ecdh_gen='{ "version": 1 , "algorithm":"ECDH", "curve":"secp256k1", "operation":"gen"}'
ecdh(ecdh_gen)
```

In this example we generate keys for A and B, and we make a key exchange between A and B.

On *"curve"* can be one of *{"brainpoolP512r1","secp521r1","brainpoolP384r1","secp384r1","brainpoolP320r1","brainpoolP256r1", "secp256k1","sect571r1","sect571k1","sect409r1","sect409k1","sect283r1","sect283k1"}*

Json to gen

```javascript
{ "version": 1 , "algorithm":"ECDH", "curve":"curve flavor", "operation":"gen"}
```

Json to key agreetment

```javascript
{ "version":1 , "algorithm":"ECDH","family": "", "privkey":" your hex privkey",
"sharedpub":"your partnert hex pubkey", "operation":"agree","curve":"curve flavor"}
```


---

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