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+.Dd $Mdocdate: November 2 2016 $
+.Dt DH_GENERATE_KEY 3
+.Os
+.Sh NAME
+.Nm DH_generate_key ,
+.Nm DH_compute_key
+.Nd perform Diffie-Hellman key exchange
+.Sh SYNOPSIS
+.In openssl/dh.h
+.Ft int
+.Fo DH_generate_key
+.Fa "DH *dh"
+.Fc
+.Ft int
+.Fo DH_compute_key
+.Fa "unsigned char *key"
+.Fa "BIGNUM *pub_key"
+.Fa "DH *dh"
+.Fc
+.Sh DESCRIPTION
+.Fn DH_generate_key
+performs the first step of a Diffie-Hellman key exchange by generating
+private and public DH values.
+By calling
+.Fn DH_compute_key ,
+these are combined with the other party's public value to compute the
+shared key.
+.Pp
+.Fn DH_generate_key
+expects
+.Fa dh
+to contain the shared parameters
+.Sy dh->p
+and
+.Sy dh->g .
+It generates a random private DH value unless
+.Sy dh->priv_key
+is already set, and computes the corresponding public value
+.Sy dh->pub_key ,
+which can then be published.
+.Pp
+.Fn DH_compute_key
+computes the shared secret from the private DH value in
+.Fa dh
+and the other party's public value in
+.Fa pub_key
+and stores it in
+.Fa key .
+.Fa key
+must point to
+.Fn DH_size dh
+bytes of memory.
+.Sh RETURN VALUES
+.Fn DH_generate_key
+returns 1 on success, 0 otherwise.
+.Pp
+.Fn DH_compute_key
+returns the size of the shared secret on success, -1 on error.
+.Pp
+The error codes can be obtained by
+.Xr ERR_get_error 3 .
+.Sh SEE ALSO
+.Xr dh 3 ,
+.Xr DH_size 3 ,
+.Xr ERR_get_error 3 ,
+.Xr rand 3
+.Sh HISTORY
+.Fn DH_generate_key
+and
+.Fn DH_compute_key
+are available in all versions of SSLeay and OpenSSL.