我有der格式的证书，使用此命令从中生成一个公共密钥：

openssl x509 -inform der -in ejbcacert.cer -noout -pubkey > pub1key.pub

结果如下：

-----BEGIN PUBLIC KEY-----
MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQC7vbqajDw4o6gJy8UtmIbkcpnk
O3Kwc4qsEnSZp/TR+fQi62F79RHWmwKOtFmwteURgLbj7D/WGuNLGOfa/2vse3G2
eHnHl5CB8ruRX9fBl/KgwCVr2JaEuUm66bBQeP5XeBotdR4cvX38uPYivCDdPjJ1
QWPdspTBKcxeFbccDwIDAQAB
-----END PUBLIC KEY-----

我如何获得这样的公钥？是从证书还是从这个公钥？

ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAAAgQC7vbqajDw4o6gJy8UtmIbkcpnkO3Kwc4qsEnSZp/TR+fQi62F79RHWmwKOtFmwteURgLbj7D/WGuNLGOfa/2vse3G2eHnHl5CB8ruRX9fBl/KgwCVr2JaEuUm66bBQeP5XeBotdR4cvX38uPYivCDdPjJ1QWPdspTBKcxeFbccDw==

这是通过以下命令获得的：

ssh-keygen -y -f private_key1.pem > public_key1.pub

无需编译内容。您可以使用ssh-keygen：

ssh-keygen -f pub1key.pub -i

将从opensl格式读取公钥，pub1key.pub并以OpenSSH格式输出。

注意：在某些情况下，您将需要指定输入格式：

ssh-keygen -f pub1key.pub -i -mPKCS8

来自ssh-keygen文档（来自man ssh-keygen）：

-m key_format为-i（导入）或-e（导出）转换选项指定密钥格式。支持的密钥格式为：“ RFC4716”（RFC 4716 / SSH2公钥或私钥），“ PKCS8”（PEM PKCS8公钥）或“ PEM”（PEM公钥）。默认转换格式为“ RFC4716”。

无需脚本或其他“招数”：openssl和ssh-keygen足够。我假设密钥没有密码（这很不好）。

生成RSA对

以下所有方法均以相同格式提供RSA密钥对

1. 与openssl（man genrsa）

   openssl genrsa -out dummy-genrsa.pem 2048
   

   在OpenSSL v1.0.1中genrsa 被取代，genpkey因此这是执行此操作的新方法（man genpkey）：

   openssl genpkey -algorithm RSA -out dummy-genpkey.pem -pkeyopt rsa_keygen_bits:2048
   

2. 使用ssh-keygen

   ssh-keygen -t rsa -b 2048 -f dummy-ssh-keygen.pem -N '' -C "Test Key"
   

将DER转换为PEM

如果您具有DER格式的RSA密钥对，则可能需要将其转换为PEM以允许以下格式转换：

代：

openssl genpkey -algorithm RSA -out genpkey-dummy.cer -outform DER -pkeyopt rsa_keygen_bits:2048

转换：

openssl rsa -inform DER -outform PEM -in genpkey-dummy.cer -out dummy-der2pem.pem

从PEM格式的RSA对中提取公钥

2. PEM格式：

   openssl rsa -in dummy-xxx.pem -pubout
   

3. OpenSSH v2格式，请参见：

   ssh-keygen -y -f dummy-xxx.pem
   

笔记

操作系统和软件版本：

[user@test1 ~]# cat /etc/redhat-release ; uname -a ; openssl version
CentOS release 6.5 (Final)
Linux test1.example.local 2.6.32-431.el6.x86_64 #1 SMP Fri Nov 22 03:15:09 UTC 2013 x86_64 x86_64 x86_64 GNU/Linux
OpenSSL 1.0.1e-fips 11 Feb 2013

参考文献：

• Sysmic.org在GnuPG，OpenSsh和OpenSSL之间转换密钥

为了回答我自己的问题，在openssl邮件列表上发布后得到以下信息：

这是从OpenSSL公钥转换为OpenSSH公钥的C代码。您可以从此链接中获取代码并自己编译：

static unsigned char pSshHeader[11] = { 0x00, 0x00, 0x00, 0x07, 0x73, 0x73, 0x68, 0x2D, 0x72, 0x73, 0x61};

static int SshEncodeBuffer(unsigned char *pEncoding, int bufferLen, unsigned char* pBuffer)
{
   int adjustedLen = bufferLen, index;
   if (*pBuffer & 0x80)
   {
      adjustedLen++;
      pEncoding[4] = 0;
      index = 5;
   }
   else
   {
      index = 4;
   }
   pEncoding[0] = (unsigned char) (adjustedLen >> 24);
   pEncoding[1] = (unsigned char) (adjustedLen >> 16);
   pEncoding[2] = (unsigned char) (adjustedLen >>  8);
   pEncoding[3] = (unsigned char) (adjustedLen      );
   memcpy(&pEncoding[index], pBuffer, bufferLen);
   return index + bufferLen;
}

int main(int argc, char**  argv)
{
   int iRet = 0;
   int nLen = 0, eLen = 0;
   int encodingLength = 0;
   int index = 0;
   unsigned char *nBytes = NULL, *eBytes = NULL;
   unsigned char* pEncoding = NULL;
   FILE* pFile = NULL;
   EVP_PKEY *pPubKey = NULL;
   RSA* pRsa = NULL;
   BIO *bio, *b64;

   ERR_load_crypto_strings(); 
   OpenSSL_add_all_algorithms();

   if (argc != 3)
   {
      printf("usage: %s public_key_file_name ssh_key_description\n", argv[0]);
      iRet = 1;
      goto error;
   }

   pFile = fopen(argv[1], "rt");
   if (!pFile)
   {
      printf("Failed to open the given file\n");
      iRet = 2;
      goto error;
   }

   pPubKey = PEM_read_PUBKEY(pFile, NULL, NULL, NULL);
   if (!pPubKey)
   {
      printf("Unable to decode public key from the given file: %s\n", ERR_error_string(ERR_get_error(), NULL));
      iRet = 3;
      goto error;
   }

   if (EVP_PKEY_type(pPubKey->type) != EVP_PKEY_RSA)
   {
      printf("Only RSA public keys are currently supported\n");
      iRet = 4;
      goto error;
   }

   pRsa = EVP_PKEY_get1_RSA(pPubKey);
   if (!pRsa)
   {
      printf("Failed to get RSA public key : %s\n", ERR_error_string(ERR_get_error(), NULL));
      iRet = 5;
      goto error;
   }

   // reading the modulus
   nLen = BN_num_bytes(pRsa->n);
   nBytes = (unsigned char*) malloc(nLen);
   BN_bn2bin(pRsa->n, nBytes);

   // reading the public exponent
   eLen = BN_num_bytes(pRsa->e);
   eBytes = (unsigned char*) malloc(eLen);
   BN_bn2bin(pRsa->e, eBytes);

   encodingLength = 11 + 4 + eLen + 4 + nLen;
   // correct depending on the MSB of e and N
   if (eBytes[0] & 0x80)
      encodingLength++;
   if (nBytes[0] & 0x80)
      encodingLength++;

   pEncoding = (unsigned char*) malloc(encodingLength);
   memcpy(pEncoding, pSshHeader, 11);

   index = SshEncodeBuffer(&pEncoding[11], eLen, eBytes);
   index = SshEncodeBuffer(&pEncoding[11 + index], nLen, nBytes);

   b64 = BIO_new(BIO_f_base64());
   BIO_set_flags(b64, BIO_FLAGS_BASE64_NO_NL);
   bio = BIO_new_fp(stdout, BIO_NOCLOSE);
   BIO_printf(bio, "ssh-rsa ");
   bio = BIO_push(b64, bio);
   BIO_write(bio, pEncoding, encodingLength);
   BIO_flush(bio);
   bio = BIO_pop(b64);
   BIO_printf(bio, " %s\n", argv[2]);
   BIO_flush(bio);
   BIO_free_all(bio);
   BIO_free(b64);

error:
   if (pFile)
      fclose(pFile);
   if (pRsa)
      RSA_free(pRsa);
   if (pPubKey)
      EVP_PKEY_free(pPubKey);
   if (nBytes)
      free(nBytes);
   if (eBytes)
      free(eBytes);
   if (pEncoding)
      free(pEncoding);

   EVP_cleanup();
   ERR_free_strings();
   return iRet;
}

ssh-keygen -i -m PKCS8 -f public-key.pem

ssh-keygen -f private.pem -y > public.pub

我做了

ssh-keygen -i -f $ sshkeysfile >>认证密钥

信誉在这里

以下脚本将获取以base64编码的DER格式的ci.jenkins-ci.org公共密钥证书，并将其转换为OpenSSH公共密钥文件。该代码假定使用2048位RSA密钥，并且从Ian Boyd的答案中汲取了很多东西。在Jenkins Wiki上对本文的评论中，我已经解释了它的工作原理。

echo -n "ssh-rsa " > jenkins.pub
curl -sfI https://ci.jenkins-ci.org/ | grep X-Instance-Identity | tr -d \\r | cut -d\  -f2 | base64 -d | dd bs=1 skip=32 count=257 status=none | xxd -p -c257 | sed s/^/00000007\ 7373682d727361\ 00000003\ 010001\ 00000101\ / | xxd -p -r | base64 -w0 >> jenkins.pub
echo >> jenkins.pub

FWIW，此BASH脚本将采用PEM或DER格式的X.509证书或OpenSSL公共密钥文件（也为PEM格式）作为第一个参数，并对OpenSSH RSA公共密钥进行分类。这扩展了@mkalkov的上述答案。的要求是cat，grep，tr，dd，xxd，sed，xargs，file，uuidgen，base64，openssl，当然（1.0+） bash。除了openssl（包含base64）以外，所有其他东西都可以保证是任何现代Linux系统上基本安装的一部分，但可能除外xxd（Fedora在vim-common软件包中显示）。如果有人想清理它并使它变得更好，请告诫。

#!/bin/bash
#
# Extract a valid SSH format public key from an X509 public certificate.
#

# Variables:
pubFile=$1
fileType="no"
pkEightTypeFile="$pubFile"
tmpFile="/tmp/`uuidgen`-pkEightTypeFile.pk8"

# See if a file was passed:
[ ! -f "$pubFile" ] && echo "Error, bad or no input file $pubFile." && exit 1

# If it is a PEM format X.509 public cert, set $fileType appropriately:
pemCertType="X$(file $pubFile | grep 'PEM certificate')"
[ "$pemCertType" != "X" ] && fileType="PEM"

# If it is an OpenSSL PEM-format PKCS#8-style public key, set $fileType appropriately:
pkEightType="X$(grep -e '-BEGIN PUBLIC KEY-' $pubFile)"
[ "$pkEightType" != "X" ] && fileType="PKCS"

# If this is a file we can't recognise, try to decode a (binary) DER-format X.509 cert:
if [ "$fileType" = "no" ]; then
        openssl x509 -in $pubFile -inform DER -noout
        derResult=$(echo $?)
        [ "$derResult" = "0" ] && fileType="DER"
fi

# Exit if not detected as a file we can use:
[ "$fileType" = "no" ] && echo "Error, input file not of type X.509 public certificate or OpenSSL PKCS#8-style public key (not encrypted)." && exit 1

# Convert the X.509 public cert to an OpenSSL PEM-format PKCS#8-style public key:
if [ "$fileType" = "PEM" -o "$fileType" = "DER" ]; then
        openssl x509 -in $pubFile -inform $fileType -noout -pubkey > $tmpFile
        pkEightTypeFile="$tmpFile"
fi

# Build the string:
# Front matter:
frontString="$(echo -en 'ssh-rsa ')"

# Encoded modulus and exponent, with appropriate pointers:
encodedModulus="$(cat $pkEightTypeFile | grep -v -e "----" | tr -d '\n' | base64 -d | dd bs=1 skip=32 count=257 status=none | xxd -p -c257 | sed s/^/00000007\ 7373682d727361\ 00000003\ 010001\ 00000101\ / | xxd -p -r | base64 -w0 )"

# Add a comment string based on the filename, just to be nice:
commentString=" $(echo $pubFile | xargs basename | sed -e 's/\.crt\|\.cer\|\.pem\|\.pk8\|\.der//')"

# Give the user a string:
echo $frontString $encodedModulus $commentString

# cleanup:
rm -f $tmpFile