OpenSSL/Diffie-Hellman 引數

要使用完美前向保密密碼套件，您必須設定 Diffie-Hellman 引數（在伺服器端），否則 PFS 密碼套件將被靜默忽略。

Diffie-Hellman

SSL_CTX_set_tmp_dh 用於為上下文設定 Diffie-Hellman 引數。使用此函式獲取 Diffie-Hellman 引數的最簡單方法之一是使用dhparam 命令列程式（帶有 -C 選項）生成隨機的 Diffie-Hellman 引數，並將生成的程式碼片段嵌入到您的程式中。例如，openssl dhparam -C 2236 可能導致

#ifndef HEADER_DH_H
#include <openssl/dh.h>
#endif
DH *get_dh2236()
	{
	static unsigned char dh2236_p[]={
		0x0F,0x52,0xE5,0x24,0xF5,0xFA,0x9D,0xDC,0xC6,0xAB,0xE6,0x04,
		0xE4,0x20,0x89,0x8A,0xB4,0xBF,0x27,0xB5,0x4A,0x95,0x57,0xA1,
		0x06,0xE7,0x30,0x73,0x83,0x5E,0xC9,0x23,0x11,0xED,0x42,0x45,
		0xAC,0x49,0xD3,0xE3,0xF3,0x34,0x73,0xC5,0x7D,0x00,0x3C,0x86,
		0x63,0x74,0xE0,0x75,0x97,0x84,0x1D,0x0B,0x11,0xDA,0x04,0xD0,
		0xFE,0x4F,0xB0,0x37,0xDF,0x57,0x22,0x2E,0x96,0x42,0xE0,0x7C,
		0xD7,0x5E,0x46,0x29,0xAF,0xB1,0xF4,0x81,0xAF,0xFC,0x9A,0xEF,
		0xFA,0x89,0x9E,0x0A,0xFB,0x16,0xE3,0x8F,0x01,0xA2,0xC8,0xDD,
		0xB4,0x47,0x12,0xF8,0x29,0x09,0x13,0x6E,0x9D,0xA8,0xF9,0x5D,
		0x08,0x00,0x3A,0x8C,0xA7,0xFF,0x6C,0xCF,0xE3,0x7C,0x3B,0x6B,
		0xB4,0x26,0xCC,0xDA,0x89,0x93,0x01,0x73,0xA8,0x55,0x3E,0x5B,
		0x77,0x25,0x8F,0x27,0xA3,0xF1,0xBF,0x7A,0x73,0x1F,0x85,0x96,
		0x0C,0x45,0x14,0xC1,0x06,0xB7,0x1C,0x75,0xAA,0x10,0xBC,0x86,
		0x98,0x75,0x44,0x70,0xD1,0x0F,0x20,0xF4,0xAC,0x4C,0xB3,0x88,
		0x16,0x1C,0x7E,0xA3,0x27,0xE4,0xAD,0xE1,0xA1,0x85,0x4F,0x1A,
		0x22,0x0D,0x05,0x42,0x73,0x69,0x45,0xC9,0x2F,0xF7,0xC2,0x48,
		0xE3,0xCE,0x9D,0x74,0x58,0x53,0xE7,0xA7,0x82,0x18,0xD9,0x3D,
		0xAF,0xAB,0x40,0x9F,0xAA,0x4C,0x78,0x0A,0xC3,0x24,0x2D,0xDB,
		0x12,0xA9,0x54,0xE5,0x47,0x87,0xAC,0x52,0xFE,0xE8,0x3D,0x0B,
		0x56,0xED,0x9C,0x9F,0xFF,0x39,0xE5,0xE5,0xBF,0x62,0x32,0x42,
		0x08,0xAE,0x6A,0xED,0x88,0x0E,0xB3,0x1A,0x4C,0xD3,0x08,0xE4,
		0xC4,0xAA,0x2C,0xCC,0xB1,0x37,0xA5,0xC1,0xA9,0x64,0x7E,0xEB,
		0xF9,0xD3,0xF5,0x15,0x28,0xFE,0x2E,0xE2,0x7F,0xFE,0xD9,0xB9,
		0x38,0x42,0x57,0x03,
		};
	static unsigned char dh2236_g[]={
		0x02,
		};
	DH *dh;

	if ((dh=DH_new()) == NULL) return(NULL);
	dh->p=BN_bin2bn(dh2236_p,sizeof(dh2236_p),NULL);
	dh->g=BN_bin2bn(dh2236_g,sizeof(dh2236_g),NULL);
	if ((dh->p == NULL) || (dh->g == NULL))
		{ DH_free(dh); return(NULL); }
	return(dh);
	}

然後可以像這樣使用

DH *dh = get_dh2236 ();
if (1 != SSL_CTX_set_tmp_dh (ctx, dh))
  error ();
DH_free (dh);

務必選擇與您想要實現的安全級別匹配的位長度，但請記住，長度超過 2236 位的 Diffie-Hellman 引數可能與舊版本的 NSS 不相容。

橢圓曲線 Diffie-Hellman

對於橢圓曲線 Diffie-Hellman，您可以執行以下操作

EC_KEY *ecdh = EC_KEY_new_by_curve_name (NID_X9_62_prime256v1);
if (! ecdh)
  error ();
if (1 != SSL_CTX_set_tmp_ecdh (ctx, ecdh))
  error ();
EC_KEY_free (ecdh);

或者，在 OpenSSL 1.0.2（截至 2013 年 2 月尚未釋出）及更高版本中，您應該能夠執行以下操作

SSL_CTX_set_ecdh_auto (ctx, 1)