C# read der encoded private key

Question

How can I get the fields from ASN1 DER format private key? Is there a library to decode and get the fields separately?

I need to extract the modulus, exponent and all the other fields.

Or maybe is there a way to convert it to .net xml format?

Have a look at the [BouncyCastle](http://www.bouncycastle.org/csharp/) library. I've used it on a previous project for similar sorts of things. — Mike Goatly, Apr 07 '11 at 09:46

score 3 · Answer 1 · answered Sep 22 '17 at 14:58

The usual private key you have comes as PEM DER ASN.1 as:

It is the BEGIN PRIVATE KEY header that tells you this is going to be data in the PrivateKeyInfo format.

PrivateKeyInfo ::= SEQUENCE {
    version                   Version,
    privateKeyAlgorithm       PrivateKeyAlgorithmIdentifier,
    privateKey                PrivateKey,
    attributes           [0]  IMPLICIT Attributes OPTIONAL 
}

The PrivateKeyAlgorithmIdentifier tells you what kind of private key is to follow (e.g. EC, RSA, DH). In the case of RSA the Algorithm ID is

1.2.840.113549.1.1.1: rsaEncryption (PKCS #1)

This means it has the following structure:

  RSAPrivateKey ::= SEQUENCE {
      version           Version,
      modulus           INTEGER,  -- n
      publicExponent    INTEGER,  -- e
      privateExponent   INTEGER,  -- d
      prime1            INTEGER,  -- p
      prime2            INTEGER,  -- q
      exponent1         INTEGER,  -- d mod (p-1)
      exponent2         INTEGER,  -- d mod (q-1)
      coefficient       INTEGER,  -- (inverse of q) mod p
      otherPrimeInfos   OtherPrimeInfos OPTIONAL
  }

The data is base64 encoded, which we can decode:

30 82 04 be 02 01 00 30 0d 06 09 2a 86 48 86 f7 0d 01 01 01 05 00 04 82 04 a8 30 82 04 a4 02 01 00 02 82 01 01 00 bb 75 3c 47 bf 36 68 10 a6 63 64 98 98 33 6c 4b d2 86 ab 27 22 d6 22 d5 66 06 0e 94 30 d2 7f 38 a6 19 f3 7f be 90 24 08 c1 33 3c 30 b0 7c 14 10 42 fa ac c6 3b ce f9 e4 84 4d b9 7a 1d a7 35 ee 71 7c b5 fb cd d4 92 64 70 61 5f 7b 16 f1 b1 11 4b 99 fd f9 0e 69 dd 18 e9 48 88 43 59 92 45 68 61 d2 d7 86 71 77 46 f0 b2 82 bf c1 ec ad 20 a1 8e 70 36 a1 9b f3 1a 2a a5 4f 93 9f 35 dc 9e 72 5b 59 cb c1 4e c9 e1 eb 4a d3 3e e0 c0 fd 57 6d 0a d8 6a 7b 57 bb 3c b3 04 d2 30 58 af d2 24 ef b8 f8 24 d1 5c 68 24 2f 07 e7 25 90 fe a4 29 14 2d 8c 7f ff d2 df 73 28 32 9b 03 03 af e3 2e 2e 92 9c c7 a7 12 22 29 f5 97 56 ac bb 76 47 f7 d7 1e fe c5 02 89 61 a1 0f 18 ea e5 4d 32 fd ec 9a f3 02 2f 78 ec f2 f4 f8 83 85 09 84 f6 6a e9 d8 45 b7 ab 79 69 8b 31 5d 85 12 1e 9e 05 01 c4 9f 02 03 01 00 01 02 82 01 00 76 b3 7e cf 43 c2 54 d5 2e 37 43 ec e8 7b af 78 b7 bf b4 c3 1c 69 12 37 a4 d9 f3 03 5d 82 fd 32 46 e3 a9 ef db 20 74 e0 e2 4d ea 30 3e a0 e3 27 84 f2 2c d3 7d ed cb 09 2b c9 f7 c7 de dd 11 e6 82 10 61 40 28 8f 11 7f ee 35 8a 7b 6c 04 f1 85 ad 24 be d0 a5 92 dd 81 37 bf 49 21 b4 a7 4d b2 12 37 ab 68 23 93 4e e5 7d 74 13 ae dd 8a a7 5e 05 cf 02 99 05 22 44 10 7b 0b 4f c4 02 1c 48 6b b4 b6 c5 f9 a4 03 37 6a 88 e4 4b 08 17 cc 70 0a 37 4d c2 5f 9b 9b 62 44 4c b0 c9 71 ff 5d 3f 80 d0 78 c7 63 95 74 f0 12 e4 27 ef cd fd 6f 40 89 6a 13 25 a7 ac 69 da cd 0e 80 56 26 db f5 91 d9 8e 37 16 f8 70 7d 0b fc 6b d3 15 ce 5e cd df a2 4f ef a5 16 3d 87 a6 f8 6c 7b b6 37 fe 3b df 9a 75 03 f4 cf 76 7b 2d f0 5d 61 a4 80 26 78 ba e7 4c a5 50 16 24 18 38 c5 32 2d ab d3 23 e5 b3 89 02 81 81 00 f1 53 67 ea 82 13 3d 54 89 4d 12 ee 6a a0 24 7b 56 3f 31 87 5b 2e d0 73 81 76 f2 f2 84 d5 70 b8 68 28 43 bf 41 9b 20 e6 42 a1 2b b9 a5 13 c4 01 64 a2 b0 89 1c 09 4e ef 24 cb 37 a6 79 a6 81 e3 3e 21 a6 79 2b 8f 78 12 ab 89 49 f9 09 fb 16 53 42 f9 fb 50 51 5f 0f 90 be 6d 82 50 93 b8 4c e3 9a 66 0e b4 bb 18 ae 39 bc 1b 4a 55 69 10 16 79 a6 00 f6 09 6d 9a 99 a6 c0 b8 cf cd da 6f 6c 5d 02 81 81 00 c6 db 4b e8 5b 30 81 60 f7 d4 4e 73 e0 a5 b5 56 33 1b e1 51 06 5b 64 d1 0d ee ac 83 65 a0 5e ad c5 02 af bc 84 f6 8b 53 8d 62 86 87 21 06 78 f1 f9 a9 7d 60 55 52 98 9f 79 1a 86 91 74 77 27 96 fa 56 90 db 3d e5 59 16 e8 2d 95 ae 27 9a 50 c1 9e 41 b7 9a 8d 27 1d 93 22 29 53 71 74 f5 f9 19 b4 46 aa 8b 62 5d d1 57 ce 96 5d dc 8b 6e 4c 5e f4 1f c5 89 07 48 33 fe 09 24 f7 23 07 13 c5 2b 02 81 80 2e 1d ee 41 d6 51 ae ea b4 c2 51 d7 d5 f0 7c 88 45 57 16 33 f3 ac e2 90 f0 30 b7 04 b9 75 c0 70 bd 16 d4 bb 7b e2 15 4b 6b 78 39 4e e4 c8 fe 2f f5 f7 51 1d 22 8a 74 d7 26 84 df 41 a5 05 b8 d4 a0 4e f5 ed 39 f1 d4 d4 5c 8b 83 e3 5f 90 e8 17 49 39 54 59 68 f3 6d 9a 0f 8a 05 d9 38 21 84 30 0a 95 6e 42 03 6f 17 fc 58 82 2e 96 5b d9 83 32 04 13 32 f1 62 4c a5 08 44 d4 0c 82 1e 38 24 d1 02 81 81 00 89 ec 2a 0e e3 c8 95 c3 ba c0 7f 15 71 f7 9c f9 47 83 8b d8 55 cf 67 f2 73 76 5a 22 dc 86 c9 84 3e c3 a9 3d d8 fe e3 0d b5 5f 63 ad 2f a3 bc 99 20 2f 85 2d 1e a0 a6 08 dd c7 1f 14 9d b1 d3 3c ad 2f 03 53 7c ef a8 c5 f1 8d 44 66 c1 43 0f c5 ea cc eb da 7f 12 65 39 da 94 cd 32 41 0c 25 94 c5 6b c9 f7 d8 e6 f7 3e ae a3 ae 40 3c 58 e9 11 66 c2 ee 90 27 03 d6 43 d8 f5 d1 8f 72 e6 2c 77 02 81 81 00 af cf 22 dc 29 75 b6 e3 d8 6e 81 25 e7 42 80 1f ca 6b b1 fa 92 be f1 8c 46 d6 be 35 c0 f7 34 f3 4a 74 bd 0b 1b 2a 54 ec 96 75 11 22 8c e1 9d 82 49 24 df 01 41 e2 84 5c a3 c6 48 95 ca f4 1e 37 a5 44 8e 9a 1e 9a 01 75 72 07 ae 2c b1 5d b3 52 6d 78 7c 24 ca 7c 96 39 81 bb 92 aa af 6c 54 8d 0b 0e 4d e9 57 e7 1f d5 5a fa a6 c8 8f 0c 4c 59 33 ea 9d 50 61 43 f2 a9 3c 5f 66 fb 9d b2 bb 0e

Which knowing it is DER ASN.1, we can start to decode:

SEQUENCE (0x4be bytes): 30 82 04 be
- INTEGER (1 byte): 02 01
  - Version: 0 00
- SEQUENCE (0x0d bytes): 30 0d
  - PrivateKeyAlgorithmIdentifier: 1.2.840.113549.1.1.1 06 09 2a 86 48 86 f7 0d 01 01 01
  - null (0 bytes): 05 00
- OCTET STRING (0x04a8 bytes): 04 82 04 a8
  - SEQUENCE (0x04a4 bytes) 30 82 04 a4
    - INTEGER (1 byte) 02 01
      - Version: 0 00
    - INTEGER (0x0101 bytes) 02 82 01 01
      - modulus 00 bb 75 3c 47 bf 36 68 10 a6 63 64 98 98 33 6c 4b d2 86 ab 27 22 d6 22 d5 66 06 0e 94 30 d2 7f 38 a6 19 f3 7f be 90 24 08 c1 33 3c 30 b0 7c 14 10 42 fa ac c6 3b ce f9 e4 84 4d b9 7a 1d a7 35 ee 71 7c b5 fb cd d4 92 64 70 61 5f 7b 16 f1 b1 11 4b 99 fd f9 0e 69 dd 18 e9 48 88 43 59 92 45 68 61 d2 d7 86 71 77 46 f0 b2 82 bf c1 ec ad 20 a1 8e 70 36 a1 9b f3 1a 2a a5 4f 93 9f 35 dc 9e 72 5b 59 cb c1 4e c9 e1 eb 4a d3 3e e0 c0 fd 57 6d 0a d8 6a 7b 57 bb 3c b3 04 d2 30 58 af d2 24 ef b8 f8 24 d1 5c 68 24 2f 07 e7 25 90 fe a4 29 14 2d 8c 7f ff d2 df 73 28 32 9b 03 03 af e3 2e 2e 92 9c c7 a7 12 22 29 f5 97 56 ac bb 76 47 f7 d7 1e fe c5 02 89 61 a1 0f 18 ea e5 4d 32 fd ec 9a f3 02 2f 78 ec f2 f4 f8 83 85 09 84 f6 6a e9 d8 45 b7 ab 79 69 8b 31 5d 85 12 1e 9e 05 01 c4 9f
    - INTEGER (3 bytes) 02 03
      - publicExponent: 01 00 01
    - INTEGER (0x0100 bytes) 02 82 01 00
      - privateExponent: 76 b3 7e cf 43 c2 54 d5 2e 37 43 ec e8 7b af 78 b7 bf b4 c3 1c 69 12 37 a4 d9 f3 03 5d 82 fd 32 46 e3 a9 ef db 20 74 e0 e2 4d ea 30 3e a0 e3 27 84 f2 2c d3 7d ed cb 09 2b c9 f7 c7 de dd 11 e6 82 10 61 40 28 8f 11 7f ee 35 8a 7b 6c 04 f1 85 ad 24 be d0 a5 92 dd 81 37 bf 49 21 b4 a7 4d b2 12 37 ab 68 23 93 4e e5 7d 74 13 ae dd 8a a7 5e 05 cf 02 99 05 22 44 10 7b 0b 4f c4 02 1c 48 6b b4 b6 c5 f9 a4 03 37 6a 88 e4 4b 08 17 cc 70 0a 37 4d c2 5f 9b 9b 62 44 4c b0 c9 71 ff 5d 3f 80 d0 78 c7 63 95 74 f0 12 e4 27 ef cd fd 6f 40 89 6a 13 25 a7 ac 69 da cd 0e 80 56 26 db f5 91 d9 8e 37 16 f8 70 7d 0b fc 6b d3 15 ce 5e cd df a2 4f ef a5 16 3d 87 a6 f8 6c 7b b6 37 fe 3b df 9a 75 03 f4 cf 76 7b 2d f0 5d 61 a4 80 26 78 ba e7 4c a5 50 16 24 18 38 c5 32 2d ab d3 23 e5 b3 89
    - INTEGER (0x81 bytes) 02 81 81
      - prime1: 00 f1 53 67 ea 82 13 3d 54 89 4d 12 ee 6a a0 24 7b 56 3f 31 87 5b 2e d0 73 81 76 f2 f2 84 d5 70 b8 68 28 43 bf 41 9b 20 e6 42 a1 2b b9 a5 13 c4 01 64 a2 b0 89 1c 09 4e ef 24 cb 37 a6 79 a6 81 e3 3e 21 a6 79 2b 8f 78 12 ab 89 49 f9 09 fb 16 53 42 f9 fb 50 51 5f 0f 90 be 6d 82 50 93 b8 4c e3 9a 66 0e b4 bb 18 ae 39 bc 1b 4a 55 69 10 16 79 a6 00 f6 09 6d 9a 99 a6 c0 b8 cf cd da 6f 6c 5d
    - INTEGER (0x81 bytes) 02 81 81
      - prime2: 00 c6 db 4b e8 5b 30 81 60 f7 d4 4e 73 e0 a5 b5 56 33 1b e1 51 06 5b 64 d1 0d ee ac 83 65 a0 5e ad c5 02 af bc 84 f6 8b 53 8d 62 86 87 21 06 78 f1 f9 a9 7d 60 55 52 98 9f 79 1a 86 91 74 77 27 96 fa 56 90 db 3d e5 59 16 e8 2d 95 ae 27 9a 50 c1 9e 41 b7 9a 8d 27 1d 93 22 29 53 71 74 f5 f9 19 b4 46 aa 8b 62 5d d1 57 ce 96 5d dc 8b 6e 4c 5e f4 1f c5 89 07 48 33 fe 09 24 f7 23 07 13 c5 2b
    - INTEGER (0x80 bytes) 02 81 80
      - exponent1: 2e 1d ee 41 d6 51 ae ea b4 c2 51 d7 d5 f0 7c 88 45 57 16 33 f3 ac e2 90 f0 30 b7 04 b9 75 c0 70 bd 16 d4 bb 7b e2 15 4b 6b 78 39 4e e4 c8 fe 2f f5 f7 51 1d 22 8a 74 d7 26 84 df 41 a5 05 b8 d4 a0 4e f5 ed 39 f1 d4 d4 5c 8b 83 e3 5f 90 e8 17 49 39 54 59 68 f3 6d 9a 0f 8a 05 d9 38 21 84 30 0a 95 6e 42 03 6f 17 fc 58 82 2e 96 5b d9 83 32 04 13 32 f1 62 4c a5 08 44 d4 0c 82 1e 38 24 d1
    - INTEGER (0x81 bytes) 02 81 81
      - exponent2: 00 89 ec 2a 0e e3 c8 95 c3 ba c0 7f 15 71 f7 9c f9 47 83 8b d8 55 cf 67 f2 73 76 5a 22 dc 86 c9 84 3e c3 a9 3d d8 fe e3 0d b5 5f 63 ad 2f a3 bc 99 20 2f 85 2d 1e a0 a6 08 dd c7 1f 14 9d b1 d3 3c ad 2f 03 53 7c ef a8 c5 f1 8d 44 66 c1 43 0f c5 ea cc eb da 7f 12 65 39 da 94 cd 32 41 0c 25 94 c5 6b c9 f7 d8 e6 f7 3e ae a3 ae 40 3c 58 e9 11 66 c2 ee 90 27 03 d6 43 d8 f5 d1 8f 72 e6 2c 77
    - INTEGER (0x81 bytes) 02 81 81
      - coefficient: 00 af cf 22 dc 29 75 b6 e3 d8 6e 81 25 e7 42 80 1f ca 6b b1 fa 92 be f1 8c 46 d6 be 35 c0 f7 34 f3 4a 74 bd 0b 1b 2a 54 ec 96 75 11 22 8c e1 9d 82 49 24 df 01 41 e2 84 5c a3 c6 48 95 ca f4 1e 37 a5 44 8e 9a 1e 9a 01 75 72 07 ae 2c b1 5d b3 52 6d 78 7c 24 ca 7c 96 39 81 bb 92 aa af 6c 54 8d 0b 0e 4d e9 57 e7 1f d5 5a fa a6 c8 8f 0c 4c 59 33 ea 9d 50 61 43 f2 a9 3c 5f 66 fb 9d b2 bb 0e

And so you have your final RSA Private Key values:

version:         0
modulus:         236643739934412948903373669476774126683629718702123314074863910669092…
publicExponent:  65,537
privateExponent: 149846324420376321261899444735289218048490924156116627413411926527864…
prime1:          169464742892393599674909179163866779357332259972872392530945213283668…
prime2:          139641872341951706778976733766729896659299032766950485174897609653257…
exponent1:       323844002622081792320149314104745036341490947693707957956201512300634… 
exponent2:       968524849673225022756364715102416566618618114106799869329534590657009… 
coefficient:     123457366510080958921249047966574081489759226696746456882235437625391…

score 3 · Answer 2 · answered Feb 29 '12 at 21:31

If all you want is to reduce the code needed to parse ASN.1, you could have a peek at the LCLib portion of the ASN.1 Editor project.

It is a simple ASN.1 processor library.

Using the sample DER encoded test string of "test1@rsa.com" :

16 0d 74 65 73 74 31 40 72 73 61 2e 63 6f 6d

    using (var stm = new MemoryStream(new byte[] { 0x16, 0x0d, 0x74, 0x65, 0x73, 0x74, 0x31, 0x40, 0x72, 0x73, 0x61, 0x2e, 0x63, 0x6f, 0x6d }))
    {
        Asn1Parser parser = new Asn1Parser();
        parser.LoadData(stm);
        var decoded = parser.ToString();
    }

Gives the formatted output:

Offset| Len |LenByte| ======+======+=======+====
 0|    13|      1| IA5 STRING : 'test1@rsa.com'

You can walk the tree, and process the nodes as you wish.

score 0 · Accepted Answer · edited Jun 11 '14 at 19:56

0

I found answer to it, I used the code from this utility: http://www.jensign.com/opensslkey/

And the source code: OpenSSLKey

edited Jun 11 '14 at 19:56

Bill the Lizard

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answered Apr 11 '11 at 11:55

hs2d

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C# read der encoded private key

3 Answers3