title: Convert DER formatted private key file to PEM form
body: <p>I have a .prv file which is probably DER formatted private key file.
  This file is used to certificate Cable Modem.</p>
  
  <p>I want to convert this file to PEM formatted one.
  I tried with openssl tool but none of below commands works.</p>
  
  <pre><code>openssl x509 -inform der -in FILENAME.prv -out FILENAME.key
  openssl rsa -inform der -in FILENAME.prv -out FILENAME.key
  openssl pkcs8 -inform der -in FILENAME.prv -out FILENAME.key 
  </code></pre>
  
  <p>Here is some beginning of the .prv file contents.</p>
  
  <pre><code>00000000h: 30 82 02 76 02 01 00 30 0D 06 09 2A 86 48 86 F7 ; 0?v...0...*낷놑
  00000010h: 0D 01 01 01 05 00 04 82 02 60 30 82 02 5C 02 01 ; .......?`0?\..
  00000020h: 00 02 81 81 00 BB 0F 6E DE 49 59 13 4A 44 12 AF ; ..걖.?n?Y.JD.?
  00000030h: 84 F0 B7 13 18 C8 F8 43 AE 09 A6 8A 6C 9B F0 AC ; 꾭?.힉C?쫲l쏊?
  00000040h: 90 1F 48 C2 75 75 41 78 74 FA DD 08 19 E0 C0 BF ; ?H혋uAxt玹..敾?
  00000050h: CC 98 D7 72 B7 C3 8C 4A 2A B9 BC 95 B6 9A 54 17 ; ??련똉*뭡빒숿.
  00000060h: 7C 5A 57 78 E1 68 87 69 18 56 8E 5D F4 D5 36 46 ; |ZWx?뇁.V?添6F
  00000070h: DF 0F 6D 54 FC 30 B6 16 AD AF D2 C6 A8 D0 C1 F7 ; ?mT???盧ⓓ직
  </code></pre>
  
  <p>Is there anything more I can try??</p>