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I am trying to get the RSA public key info in WinHTTP. So far I've got the certificate info in CERT_CONTEXT structure. I can get encryption algorithm and others as follows:
PCCERT_CONTEXT cert;
DWORD certLen = sizeof(PCCERT_CONTEXT);
WinHttpQueryOption(hRequest, WINHTTP_OPTION_SERVER_CERT_CONTEXT, &cert, &certLen);
The encryption algorithm is got by
LPSTR pubKeyAlgo = cert->pCertInfo->SubjectPublicKeyInfo.Algorithm.pszObjId;
And we might get the public key as follows:
CRYPT_BIT_BLOB pubKey = cert->pCertInfo->SubjectPublicKeyInfo.PublicKey;
BYTE *p = pKey.pbData;
But as per the documentation, this is an encoded form:
PublicKey
BLOB containing an encoded public key.
So how to get the actual RSA public key parameters like modulus and exponent?
918
asked May 26 '14 06:05
Here's an example of extracting the modulus and exponent of a RSA Public Key using Wincrypt. The example certificate is a SSH client cert from RFC 6187. The certificate can be used for SSH's x509v3-rsa2048-sha256 signature encoding method. The OpenSSL conf file is at the end of the answer, but was adapted from How to create a self-signed certificate with OpenSSL.
RSA_PUBLIC_KEY_XX is used to cast the blob returned from CryptDecodeObject to the packed RSA structures the API returns. The name *_XX was used to avoid colliding with a future Microsoft structure name.
#include <iostream>
#include <iomanip>
#include <sstream>
#include <memory>
#include <string>
#include <vector>
#define WIN32_LEAN_AND_MEAN
#include <windows.h>
#include <wincrypt.h>
#pragma comment(lib, "kernel32")
#pragma comment(lib, "crypt32")
typedef struct _RSA_PUBLIC_KEY_XX
{
#pragma pack(push, 1)
PUBLICKEYSTRUC PublicKeyStruc;
RSAPUBKEY RsaPubKey;
BYTE RsaModulus[ANYSIZE_ARRAY];
#pragma pack(pop)
} RSA_PUBLIC_KEY_XX, *PRSA_PUBLIC_KEY_XX, *const PCRSA_PUBLIC_KEY_XX;
extern std::string pemCertificate;
void PrintErrorAndThrow(const char* fnName, DWORD dwError);
int main(int argc, char* argv[])
{
DWORD dwSize = 0;
std::vector<BYTE> asnCertificate;
std::vector<BYTE> rsaPublicKey;
BOOL bResult = CryptStringToBinary(
&pemCertificate[0],
static_cast<DWORD>(pemCertificate.size()),
CRYPT_STRING_BASE64HEADER,
NULL, &dwSize,
NULL, NULL);
if (bResult == FALSE)
PrintErrorAndThrow("CryptStringToBinary", GetLastError());
asnCertificate.resize(dwSize);
dwSize = static_cast<DWORD>(asnCertificate.size());
bResult = CryptStringToBinary(
&pemCertificate[0],
static_cast<DWORD>(pemCertificate.size()),
CRYPT_STRING_BASE64HEADER,
&asnCertificate[0], &dwSize,
NULL, NULL);
if (bResult == FALSE)
PrintErrorAndThrow("CryptStringToBinary", GetLastError());
PCCERT_CONTEXT pContext = CertCreateCertificateContext(
X509_ASN_ENCODING,
static_cast<PBYTE>(&asnCertificate[0]),
static_cast<DWORD>(asnCertificate.size()));
if (pContext == NULL)
PrintErrorAndThrow("CertCreateCertificateContext", GetLastError());
PCERT_INFO pInfo = pContext->pCertInfo;
PCERT_PUBLIC_KEY_INFO pSubjectPublicKeyInfo = &pInfo->SubjectPublicKeyInfo;
PCRYPT_BIT_BLOB pPublicKey = &pSubjectPublicKeyInfo->PublicKey;
bResult = CryptDecodeObject(
pContext->dwCertEncodingType,
RSA_CSP_PUBLICKEYBLOB,
pPublicKey->pbData,
pPublicKey->cbData,
0, // flags
NULL, &dwSize);
if (bResult == FALSE)
PrintErrorAndThrow("CryptDecodeObject", GetLastError());
rsaPublicKey.resize(dwSize);
dwSize = static_cast<DWORD>(rsaPublicKey.size());
bResult = CryptDecodeObject(
pContext->dwCertEncodingType,
RSA_CSP_PUBLICKEYBLOB,
pPublicKey->pbData,
pPublicKey->cbData,
0, // flags
&rsaPublicKey[0],
&dwSize);
if (bResult == FALSE)
PrintErrorAndThrow("CryptDecodeObject", GetLastError());
PCRSA_PUBLIC_KEY_XX pRsaPublicKey = reinterpret_cast<PCRSA_PUBLIC_KEY_XX>(&rsaPublicKey[0]);
DWORD dwModulusSize = pRsaPublicKey->RsaPubKey.bitlen/8;
DWORD dwExponent = pRsaPublicKey->RsaPubKey.pubexp;
DWORD dwMagic = pRsaPublicKey->RsaPubKey.magic;
if (dwMagic != 0x31415352 /*RSA1*/)
PrintErrorAndThrow("CryptDecodeObject", ERROR_INVALID_DATA);
// The modulus is little-endian. Iterate in reverse for big-endian.
std::ostringstream oss;
for (size_t i=dwModulusSize; i > 0; --i)
{
oss << std::hex << std::setw(2) << std::setfill('0');
oss << (unsigned int)pRsaPublicKey->RsaModulus[i-1];
if (i > 1) { oss << ":"; }
}
std::cout << "Magic: " << "0x" << std::hex << dwMagic << std::endl;
std::cout << "Exponent: " << std::dec << dwExponent << std::endl;
std::cout << "Modulus: " << oss.str() << std::endl;
if (pContext)
CertFreeCertificateContext(pContext);
return 0;
}
void PrintErrorAndThrow(const char* fnName, DWORD dwError)
{
std::ostringstream oss;
oss << fnName << " failed, error " << dwError << " (";
oss << "0x" << std::hex << dwError << ")" << std::endl;
std::cerr << oss.str() << std::endl;
throw std::runtime_error(oss.str());
}
std::string pemCertificate =
"-----BEGIN CERTIFICATE-----\r\n"
"MIIESjCCAzKgAwIBAgIUb2d597NowQ3H/4UE/qjrqzT+EPkwDQYJKoZIhvcNAQEL\r\n"
"BQAwfDELMAkGA1UEBhMCVVMxCzAJBgNVBAgMAk5ZMREwDwYDVQQHDAhOZXcgWW9y\r\n"
"azEVMBMGA1UECgwMRXhhbXBsZSwgTExDMREwDwYDVQQDDAhKb2huIERvZTEjMCEG\r\n"
"CSqGSIb3DQEJARYUam9obi5kb2VAZXhhbXBsZS5jb20wHhcNMTkwOTE3MTU1OTA1\r\n"
"WhcNMjAwOTE2MTU1OTA1WjB8MQswCQYDVQQGEwJVUzELMAkGA1UECAwCTlkxETAP\r\n"
"BgNVBAcMCE5ldyBZb3JrMRUwEwYDVQQKDAxFeGFtcGxlLCBMTEMxETAPBgNVBAMM\r\n"
"CEpvaG4gRG9lMSMwIQYJKoZIhvcNAQkBFhRqb2huLmRvZUBleGFtcGxlLmNvbTCC\r\n"
"ASIwDQYJKoZIhvcNAQEBBQADggEPADCCAQoCggEBAOd2VZa5G8clxnT90+1mkCGp\r\n"
"ufPAEXKLwX7THhIOf00NYRpumuhvMBUHFNcH6H17NHM/iauLacXsYIJlHWmTTl1t\r\n"
"0r7fxzVTA4NF8Eedpv+RGXRm3eC/e+Nz/MkdInWZ7qkp6AE9juiEop9rmQPtwM/f\r\n"
"4/LwE2fi+XyhFTwMr2zIUuEVlk1fWaabOVtHweLCWxvstWtomxN4egVY4kB634zM\r\n"
"VywMGRz4YrKzFxSaTYWt5wNoMoPRGeEKFwhBfuXmHIO9QQSxqIfBEoxQfBdppzSN\r\n"
"5qe84Gn9nFSepgmJtw6XLxm31SgMBOuKiwFbFni+oZEnRg9ssy7UYmaAaxcqfikC\r\n"
"AwEAAaOBwzCBwDAdBgNVHQ4EFgQU1nhsQ/gKlSadP9uEUNMj5ezkt7gwHwYDVR0j\r\n"
"BBgwFoAU1nhsQ/gKlSadP9uEUNMj5ezkt7gwCQYDVR0TBAIwADALBgNVHQ8EBAMC\r\n"
"B4AwHwYDVR0RBBgwFoEUam9obi5kb2VAZXhhbXBsZS5jb20wMAYJYIZIAYb4QgEN\r\n"
"BCMWIU9wZW5TU0wgR2VuZXJhdGVkIFNTSCBDZXJ0aWZpY2F0ZTATBgNVHSUEDDAK\r\n"
"BggrBgEFBQcDFTANBgkqhkiG9w0BAQsFAAOCAQEAUkCY+WX55RuqzuuRMt5hEzUh\r\n"
"xfCVLddfBxmokmsodc8qgHlsNkRLLZATyKgnFF5FGIroiNF6QcJ5QJXDZZyz2+6p\r\n"
"m0V1jHF51BtoGxBR1I1ERLT0QOJHC53R6+/OPIaADKdPoXHIpPVQhJww6e1X6CU1\r\n"
"IjIWmliqixhvId5WbU5et6ZpFNs2ZFbPGBk4RrKR5SjxwLj7Jm+THzV660xIYsow\r\n"
"/CP5ox7ga7+OFR6q4kFQldc6Ah5bRFKI8fgWHpnhlS9hB29BiMjrC/p7bm0CL2Su\r\n"
"QER4F/HCpBHBDwkweg1h9DrT62DYgqvgvRxR/j8GPL7Hqg2kLuFcHt3SkQeNZg==\r\n"
"-----END CERTIFICATE-----\r\n";
Compile the program using a Visual Studio Developer command prompt.
C:\Users\Test>cl.exe /nologo /W4 /Zi /TP /GR /EHsc cert_test.cxx /link /out:cert_test.exe
cert_test.cxx
cert_test.cxx(37) : warning C4100: 'argv' : unreferenced formal parameter
cert_test.cxx(37) : warning C4100: 'argc' : unreferenced formal parameter
And running the program results in the following.
C:\Users\Test>.\cert_test.exe
Magic: 0x31415352
Exponent: 65537
Modulus: e7:76:55:96:b9:1b:c7:25:c6:74:fd:d3:ed:66:90:21:a9:b9:f3:c0:11:72:8b:c1
:7e:d3:1e:12:0e:7f:4d:0d:61:1a:6e:9a:e8:6f:30:15:07:14:d7:07:e8:7d:7b:34:73:3f:8
9:ab:8b:69:c5:ec:60:82:65:1d:69:93:4e:5d:6d:d2:be:df:c7:35:53:03:83:45:f0:47:9d:
a6:ff:91:19:74:66:dd:e0:bf:7b:e3:73:fc:c9:1d:22:75:99:ee:a9:29:e8:01:3d:8e:e8:84
:a2:9f:6b:99:03:ed:c0:cf:df:e3:f2:f0:13:67:e2:f9:7c:a1:15:3c:0c:af:6c:c8:52:e1:1
5:96:4d:5f:59:a6:9b:39:5b:47:c1:e2:c2:5b:1b:ec:b5:6b:68:9b:13:78:7a:05:58:e2:40:
7a:df:8c:cc:57:2c:0c:19:1c:f8:62:b2:b3:17:14:9a:4d:85:ad:e7:03:68:32:83:d1:19:e1
:0a:17:08:41:7e:e5:e6:1c:83:bd:41:04:b1:a8:87:c1:12:8c:50:7c:17:69:a7:34:8d:e6:a
7:bc:e0:69:fd:9c:54:9e:a6:09:89:b7:0e:97:2f:19:b7:d5:28:0c:04:eb:8a:8b:01:5b:16:
78:be:a1:91:27:46:0f:6c:b3:2e:d4:62:66:80:6b:17:2a:7e:29
Here is a dump of the certificate using OpenSSL's x509 subcommand.
$ cat cert_test.cert.pem | openssl x509 -text -noout
Certificate:
Data:
Version: 3 (0x2)
Serial Number:
6f:67:79:f7:b3:68:c1:0d:c7:ff:85:04:fe:a8:eb:ab:34:fe:10:f9
Signature Algorithm: sha256WithRSAEncryption
Issuer: C = US, ST = NY, L = New York, O = "Example, LLC", CN = John Doe, emailAddress = [email protected]
Validity
Not Before: Sep 17 15:59:05 2019 GMT
Not After : Sep 16 15:59:05 2020 GMT
Subject: C = US, ST = NY, L = New York, O = "Example, LLC", CN = John Doe, emailAddress = [email protected]
Subject Public Key Info:
Public Key Algorithm: rsaEncryption
RSA Public-Key: (2048 bit)
Modulus:
00:e7:76:55:96:b9:1b:c7:25:c6:74:fd:d3:ed:66:
90:21:a9:b9:f3:c0:11:72:8b:c1:7e:d3:1e:12:0e:
7f:4d:0d:61:1a:6e:9a:e8:6f:30:15:07:14:d7:07:
e8:7d:7b:34:73:3f:89:ab:8b:69:c5:ec:60:82:65:
1d:69:93:4e:5d:6d:d2:be:df:c7:35:53:03:83:45:
f0:47:9d:a6:ff:91:19:74:66:dd:e0:bf:7b:e3:73:
fc:c9:1d:22:75:99:ee:a9:29:e8:01:3d:8e:e8:84:
a2:9f:6b:99:03:ed:c0:cf:df:e3:f2:f0:13:67:e2:
f9:7c:a1:15:3c:0c:af:6c:c8:52:e1:15:96:4d:5f:
59:a6:9b:39:5b:47:c1:e2:c2:5b:1b:ec:b5:6b:68:
9b:13:78:7a:05:58:e2:40:7a:df:8c:cc:57:2c:0c:
19:1c:f8:62:b2:b3:17:14:9a:4d:85:ad:e7:03:68:
32:83:d1:19:e1:0a:17:08:41:7e:e5:e6:1c:83:bd:
41:04:b1:a8:87:c1:12:8c:50:7c:17:69:a7:34:8d:
e6:a7:bc:e0:69:fd:9c:54:9e:a6:09:89:b7:0e:97:
2f:19:b7:d5:28:0c:04:eb:8a:8b:01:5b:16:78:be:
a1:91:27:46:0f:6c:b3:2e:d4:62:66:80:6b:17:2a:
7e:29
Exponent: 65537 (0x10001)
X509v3 extensions:
X509v3 Subject Key Identifier:
D6:78:6C:43:F8:0A:95:26:9D:3F:DB:84:50:D3:23:E5:EC:E4:B7:B8
X509v3 Authority Key Identifier:
keyid:D6:78:6C:43:F8:0A:95:26:9D:3F:DB:84:50:D3:23:E5:EC:E4:B7:B8
X509v3 Basic Constraints:
CA:FALSE
X509v3 Key Usage:
Digital Signature
X509v3 Subject Alternative Name:
email:[email protected]
Netscape Comment:
OpenSSL Generated SSH Certificate
X509v3 Extended Key Usage:
SSH Client
Signature Algorithm: sha256WithRSAEncryption
52:40:98:f9:65:f9:e5:1b:aa:ce:eb:91:32:de:61:13:35:21:
c5:f0:95:2d:d7:5f:07:19:a8:92:6b:28:75:cf:2a:80:79:6c:
36:44:4b:2d:90:13:c8:a8:27:14:5e:45:18:8a:e8:88:d1:7a:
41:c2:79:40:95:c3:65:9c:b3:db:ee:a9:9b:45:75:8c:71:79:
d4:1b:68:1b:10:51:d4:8d:44:44:b4:f4:40:e2:47:0b:9d:d1:
eb:ef:ce:3c:86:80:0c:a7:4f:a1:71:c8:a4:f5:50:84:9c:30:
e9:ed:57:e8:25:35:22:32:16:9a:58:aa:8b:18:6f:21:de:56:
6d:4e:5e:b7:a6:69:14:db:36:64:56:cf:18:19:38:46:b2:91:
e5:28:f1:c0:b8:fb:26:6f:93:1f:35:7a:eb:4c:48:62:ca:30:
fc:23:f9:a3:1e:e0:6b:bf:8e:15:1e:aa:e2:41:50:95:d7:3a:
02:1e:5b:44:52:88:f1:f8:16:1e:99:e1:95:2f:61:07:6f:41:
88:c8:eb:0b:fa:7b:6e:6d:02:2f:64:ae:40:44:78:17:f1:c2:
a4:11:c1:0f:09:30:7a:0d:61:f4:3a:d3:eb:60:d8:82:ab:e0:
bd:1c:51:fe:3f:06:3c:be:c7:aa:0d:a4:2e:e1:5c:1e:dd:d2:
91:07:8d:66
Here is the OpenSSL configuration file from How to create a self-signed certificate with OpenSSL tweaked for a SSH client.
# Create a self signed certificate:
# openssl req -config cert_test.conf -new -x509 -sha256 -newkey rsa:2048 \
# -nodes -keyout cert_test.key.pem -days 365 -out cert_test.cert.pem
#
# Create a signing request (notice the lack of -x509 option):
# openssl req -config cert_test.conf -new -sha256 -newkey rsa:2048 \
# -nodes -keyout cert_test.key.pem -days 365 -out cert_test.cert.pem
[ req ]
default_bits = 2048
default_keyfile = server-key.pem
distinguished_name = subject
req_extensions = req_ext
x509_extensions = x509_ext
string_mask = utf8only
# The Subject DN can be formed using X501 or RFC 4514 (see RFC 4519 for a description).
[ subject ]
countryName = Country Name (2 letter code)
countryName_default = US
stateOrProvinceName = State or Province Name (full name)
stateOrProvinceName_default = NY
localityName = Locality Name (eg, city)
localityName_default = New York
organizationName = Organization Name (eg, company)
organizationName_default = Example, LLC
commonName = Common Name (e.g. server FQDN or YOUR name)
commonName_default = John Doe
emailAddress = Email Address
emailAddress_default = [email protected]
# Section x509_ext is used when generating a self-signed certificate. I.e., openssl req -x509 ...
[ x509_ext ]
subjectKeyIdentifier = hash
authorityKeyIdentifier = keyid,issuer
basicConstraints = CA:FALSE
keyUsage = digitalSignature
subjectAltName = @alternate_names
nsComment = "OpenSSL Generated SSH Certificate"
extendedKeyUsage = secureShellClient
# Section req_ext is used when generating a certificate signing request. I.e., openssl req ...
[ req_ext ]
subjectKeyIdentifier = hash
basicConstraints = CA:FALSE
keyUsage = digitalSignature
subjectAltName = @alternate_names
nsComment = "OpenSSL Generated SSH Certificate"
extendedKeyUsage = secureShellClient
[ alternate_names ]
email = [email protected]
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