Or use another hash type for signature which can produce not more than 53 bytes of hashed data. (i.e MD5, SHA1, SHA256, SHA384) while using 512-bit keys. OpenSSL by default uses SHA512 hash for signature. Change the code to use any other hash.
512 bit(64 byte) RSA key can only encrypt 53 bytes at max. 64 - 11 byte padding and SHA512 produces 64 bytes of hashed data. Thanks, Thulasi. On Tue, Feb 26, 2013 at 11:42 PM, Viktor Dukhovni < openssl-us...@dukhovni.org> wrote: > On Tue, Feb 26, 2013 at 11:30:18PM +0530, Nayna Jain wrote: > > > Both server and client authenticate each other. And so client also sends > > the certificate. > > > > Here client certificate has RSA 512 bits and md5. Server certificates has > > RSA 1024 bits and md5. > > Bottom-line: DO NOT use 512-bit RSA moduli, they are trivially > factored on commodity hardware. > > > Both server and client are using the API SSLv23_server_method() and > > SSLv23_client_method() respectively > > > > Opensssl version used is 1.0.1c. > > > > So, when I initiate the connection from client, I get this error "SSL > > negotiation failed: error:04075070:rsa routines:RSA_sign:digest too big > for > > rsa key" on client side. > > > > Can someone please explain the reason for this error ? > > http://archives.neohapsis.com/archives/postfix/2013-02/0235.html > > The negotiated TLSv1.2 digest produces output that is too wide to be > signed with an RSA 512-bit private key. The client key should be > at least 1024-bits, and in many cases stronger. > > It is arguably the case that OpenSSL should not present a client > certificate that cannot sign using the agreed digest. One approach > is for the client to not offer ciphersuites that are too wide for > its private key. > > This said, DO NOT use 512-bit RSA keys. I'm puzzled by their apparent > popularity, why does your client have such a key? > > -- > Viktor. > ______________________________________________________________________ > OpenSSL Project http://www.openssl.org > User Support Mailing List openssl-users@openssl.org > Automated List Manager majord...@openssl.org >
