I have a certificate in der
format, from it with this command I generate a public key:
openssl x509 -inform der -in ejbcacert.cer -noout -pubkey > pub1key.pub
Which results in this:
-----BEGIN PUBLIC KEY-----
MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQC7vbqajDw4o6gJy8UtmIbkcpnk
O3Kwc4qsEnSZp/TR+fQi62F79RHWmwKOtFmwteURgLbj7D/WGuNLGOfa/2vse3G2
eHnHl5CB8ruRX9fBl/KgwCVr2JaEuUm66bBQeP5XeBotdR4cvX38uPYivCDdPjJ1
QWPdspTBKcxeFbccDwIDAQAB
-----END PUBLIC KEY-----
How can I obtain a public key like this? Either from certificate or from this public key?
ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAAAgQC7vbqajDw4o6gJy8UtmIbkcpnkO3Kwc4qsEnSZp/TR+fQi62F79RHWmwKOtFmwteURgLbj7D/WGuNLGOfa/2vse3G2eHnHl5CB8ruRX9fBl/KgwCVr2JaEuUm66bBQeP5XeBotdR4cvX38uPYivCDdPjJ1QWPdspTBKcxeFbccDw==
This was obtained with this command:
ssh-keygen -y -f private_key1.pem > public_key1.pub
To answer my own question, after posting on openssl mailing list got this:
Here is C code to convert from an OpenSSL public key to an OpenSSH public key. You can grab the code from this link and compile it yourself:
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;
}