title: Hyperledger fabric Crypto materials
body: <p>If we see the <strong>crypto-config</strong> folder in <strong>basic-network</strong> of <strong>fabric-sample</strong>, we have various certificate materials with various types:</p>
  
  <pre><code>└── example.com
  ├── ca
  │   ├── 0d46ccf0e9436c1bc3b6e2bf80cdb202c4943604f95c72ee0ff839d3ec300719_sk
  │   └── ca.example.com-cert.pem
  ├── msp
  │   ├── admincerts
  │   │   └── Admin@example.com-cert.pem
  │   ├── cacerts
  │   │   └── ca.example.com-cert.pem
  │   └── tlscacerts
  │       └── tlsca.example.com-cert.pem
  ├── orderers
  │   └── orderer.example.com
  │       ├── msp
  │       │   ├── admincerts
  │       │   │   └── Admin@example.com-cert.pem
  │       │   ├── cacerts
  │       │   │   └── ca.example.com-cert.pem
  │       │   ├── keystore
  │       │   │   └── 2fb065725bf1b7e2811c0e8ca8d37f5a951fc4cd1162a47aad8accf9ddd10291_sk
  │       │   ├── signcerts
  │       │   │   └── orderer.example.com-cert.pem
  │       │   └── tlscacerts
  │       │       └── tlsca.example.com-cert.pem
  │       └── tls
  │           ├── ca.crt
  │           ├── server.crt
  │           └── server.key
  ├── tlsca
  │   ├── 6a211ed18880b4db3867831c977809902713b8e321a5ab55ecc104dafc2eec49_sk
  │   └── tlsca.example.com-cert.pem
  └── users
      └── Admin@example.com
          ├── msp
          │   ├── admincerts
          │   │   └── Admin@example.com-cert.pem
          │   ├── cacerts
          │   │   └── ca.example.com-cert.pem
          │   ├── keystore
          │   │   └── db670eed8487a93c35ae448b9f84c2f241a7a8c87df0544fc1dc08baf7832aa0_sk
          │   ├── signcerts
          │   │   └── Admin@example.com-cert.pem
          │   └── tlscacerts
          │       └── tlsca.example.com-cert.pem
          └── tls
              ├── ca.crt
              ├── server.crt
              └── server.key
  </code></pre>
  
  <p>Can anyone explain why there are so too many of these files why are some of these files duplicated(such as <strong>ca.example.com-cert.pem</strong> have many copies) and there purpose.
  What are <strong>.pem</strong> files used for?<br>
  What are <strong>.crt</strong> files used for?<br>
  What are <strong>.key</strong> files used for?<br>
  What are ** ...._sk** files used for?  </p>
  
  <p>And why the <strong>fabcar</strong> example manage it only by using 3 files.??</p>
  
  <pre><code>fabcar/creds
  ├── 5890f0061619c06fb29dea8cb304edecc020fe63f41a6db109f1e227cc1cb2a8-priv
  ├── 5890f0061619c06fb29dea8cb304edecc020fe63f41a6db109f1e227cc1cb2a8-pub
  └── PeerAdmin
  </code></pre>
  
  <p>Thanks for your help</p>