問題描述

我有一個文件，其中有幾個 ECDSA SHA256 的公鑰.該文件如下所示:

I have got a file in which there are several public keys for ECDSA SHA256. The file looks like:

KEY_ID: 1
STATUS: VALID
-----BEGIN PUBLIC KEY-----
MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEaq6djyzkpHdX7kt8DsSt6IuSoXjp
WVlLfnZPoLaGKc/2BSfYQuFIO2hfgueQINJN3ZdujYXfUJ7Who+XkcJqHQ==
-----END PUBLIC KEY-----

KEY_ID: 2
STATUS: VALID
-----BEGIN PUBLIC KEY-----
MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAE+Y5mYZL/EEY9zGji+hrgGkeoyccK
D0/oBoSDALHc9+LXHKsxXiEV7/h6d6+fKRDb6Wtx5cMzXT9HyY+TjPeuTg==
-----END PUBLIC KEY-----

KEY_ID: 3
STATUS: VALID
-----BEGIN PUBLIC KEY-----
MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEkvgJ6sc2MM0AAFUJbVOD/i34YJJ8
ineqTN+DMjpI5q7fQNPEv9y2z/ecPl8qPus8flS4iLOOxdwGoF1mU9lwfA==
-----END PUBLIC KEY-----

我怎樣才能為這些鍵中的一個(或全部)獲取 CngKey 對象(或 CngKey 列表)?

How can I can get CngKey object (or list of CngKey) for one (or all) of these keys?

我嘗試過類似的東西

string plainTextKey = "MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEaq6djyzkpHdX7kt8DsSt6IuSoXjpWVlLfnZPoLaGKc/2BSfYQuFIO2hfgueQINJN3ZdujYXfUJ7Who+XkcJqHQ==";
byte[] publicKeyBytes = Convert.FromBase64String(plainTextKey);
CngKey ret = CngKey.Import(publicKeyBytes, CngKeyBlobFormat.EccPublicBlob);

但是 Import 方法拋出 System.Security.Cryptography.CryptographicException 無效參數.

but Import method throws System.Security.Cryptography.CryptographicException for invalid parameter.

推薦答案

EccPublicBlob 映射到 BCRYPT_ECCPUBLIC_BLOB 格式類型，不是 X.509 SubjectPublicKeyInfo.

EccPublicBlob maps to BCRYPT_ECCPUBLIC_BLOB format type, not X.509 SubjectPublicKeyInfo.

如果您的所有密鑰都在 secp256r1/NIST P-256 上，那么有一個非常簡單的 hacky 方法.

If all of your keys are on secp256r1/NIST P-256 then there's a pretty straightforward hacky approach.

您可能已經注意到，您的所有密鑰都以 MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAE 開頭.我們很快就會看到原因.

You may have noticed that all of your keys start with MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAE. We'll see why shortly.

轉換

MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEaq6djyzkpHdX7kt8DsSt6IuSoXjp
WVlLfnZPoLaGKc/2BSfYQuFIO2hfgueQINJN3ZdujYXfUJ7Who+XkcJqHQ==

到字節(或者，這里是十六進制):

to bytes (or, here, hex):

30 59 30 13 06 07 2A 86 48 CE 3D 02 01 06 08 2A 
86 48 CE 3D 03 01 07 03 42 00 04 6A AE 9D 8F 2C 
E4 A4 77 57 EE 4B 7C 0E C4 AD E8 8B 92 A1 78 E9 
59 59 4B 7E 76 4F A0 B6 86 29 CF F6 05 27 D8 42 
E1 48 3B 68 5F 82 E7 90 20 D2 4D DD 97 6E 8D 85 
DF 50 9E D6 86 8F 97 91 C2 6A 1D

這是一個 DER 編碼的 X.509 SubjectPublicKeyInfo blob.

This is a DER encoded X.509 SubjectPublicKeyInfo blob.

使用我們看到的 DER-fu

Using our DER-fu we see

// SubjectPublicKeyInfo
30 59  // SEQUENCE, 0x59 == 89 bytes of payload
   // AlgorithmIdentifier
   30 13  // SEQUENCE, 0x13 == 19 bytes of payload
      // AlgorithmIdentifier.algorithm
      06 07 2A 86 48 CE 3D 02 01  // OBJECT ID 1.2.840.10045.2.1 (id-ecPublicKey)
      // AlgorithmIdentifier.parameters
      06 08 2A 86 48 CE 3D 03 01 07 // OBJECT ID 1.2.840.10045.3.1.7 (secp256r1)
   // SubjectPublicKeyInfo.publicKey
   03 42 00  // BIT STRING, 0x42 == 66 (65) payload bytes, 0 unused bits
      // "the public key"
      04
      92F809EAC73630CD000055096D5383FE2DF860927C8A77AA4CDF83323A48E6AE
      DF40D3C4BFDCB6CFF79C3E5F2A3EEB3C7E54B888B38EC5DC06A05D6653D9707C

由于算法標識符是 id-ecPublicKey，因此參數是標識曲線的 OID(在本例中為 secp256r1/NIST P-256).和公鑰"格式來自 SEC 1 v2.0 (2.3.4 Octet-String-到橢圓曲線點轉換).

Since the algorithm identifier is id-ecPublicKey the parameters is an OID identifying the curve (in this case, secp256r1 / NIST P-256). And "the public key" is of a format from SEC 1 v2.0 (2.3.4 Octet-String-to-Elliptic-Curve-Point Conversion).

最常見的編碼是類型04，未壓縮的密鑰.(0x04 后跟 Qx 填充到必要的長度，然后 Qy 填充到必要的長度).

The most common encoding is type 04, uncompressed key. (0x04 followed by Qx padded to the necessary length followed by Qy padded to the necessary length).

因此，對于在 secp256r1 上以 04 類型編碼的所有點，字節模式都以

So, for all points encoded with type 04 on secp256r1 the byte pattern starts with

30 59 30 13 06 07 2A 86 48 CE 3D 02 01 06 08 2A 
86 48 CE 3D 03 01 07 03 42 00 04

恰好與 MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAE 的通用 base64 前綴對齊.

which happens to align to a common base64 prefix of MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAE.

CNG 想要什么 是 [32 位標識符][32 位小端長度][填充 Qx][填充 Qy].

What CNG wants is [32-bit identifier][32-bit little-endian length][padded Qx][padded Qy].

所以超級騙子的hacky版本是:

So the super-duper hacky version is:

private static readonly byte[] s_secp256r1Prefix =
    Convert.FromBase64String("MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAE");

// For ECDH instead of ECDSA, change 0x53 to 0x4B.
private static readonly byte[] s_cngBlobPrefix = { 0x45, 0x43, 0x53, 0x31, 0x20, 0, 0, 0 };

private static CngKey ImportECDsa256PublicKey(string base64)
{
    byte[] subjectPublicKeyInfo = Convert.FromBase64String(base64);

    if (subjectPublicKeyInfo.Length != 91)
        throw new InvalidOperationException();

    byte[] prefix = s_secp256r1Prefix;

    if (!subjectPublicKeyInfo.Take(prefix.Length).SequenceEqual(prefix))
        throw new InvalidOperationException();

    byte[] cngBlob = new byte[s_cngBlobPrefix.Length + 64];
    Buffer.BlockCopy(s_cngBlobPrefix, 0, cngBlob, 0, s_cngBlobPrefix.Length);

    Buffer.BlockCopy(
        subjectPublicKeyInfo,
        s_secp256r1Prefix.Length,
        cngBlob,
        s_cngBlobPrefix.Length,
        64);

    return CngKey.Import(cngBlob, CngKeyBlobFormat.EccPublicBlob);
}

要支持其他曲線，您需要將 CNG blob 的前 4 個字節更改為正確的Magic"；值，并將第 5 個字節更改為正確的長度.當然，不同的 SubjectPublicKeyInfo 前綴，64 不會是公鑰坐標長度(64 == 256/8 * 2).但所有這些都留給讀者作為練習.

To support other curves you need to change the first 4 bytes of the CNG blob to the correct "Magic" value, and change the 5th byte to be the correct length. And, of course, different SubjectPublicKeyInfo prefixes, and 64 won't be the public key coordinate length (64 == 256 / 8 * 2). But all of that is left as an exercise to the reader.

請參閱 C# 和 PHP ECDH 不匹配反過來.

這篇關于C# 從文本文件中的公鑰獲取 CngKey 對象的文章就介紹到這了，希望我們推薦的答案對大家有所幫助，也希望大家多多支持html5模板網！