1. openswan源码中支持的DH组：

2. DH组编号：

DH组编号	OAKLEY组名称	ID号
DH1	OAKLEY_GROUP_MODP768	1
DH2	OAKLEY_GROUP_MODP1024	2
DH3	OAKLEY_GROUP_GP155	3
DH4	OAKLEY_GROUP_GP185	4
DH5	OAKLEY_GROUP_MODP1536	5
DH14	OAKLEY_GROUP_MODP2048	14
DH15	OAKLEY_GROUP_MODP3072	15
DH16	OAKLEY_GROUP_MODP4096	16
DH17	OAKLEY_GROUP_MODP6144	17
DH18	OAKLEY_GROUP_MODP8192	18
DH22	OAKLEY_GROUP_DH22	22
DH23	OAKLEY_GROUP_DH23	23
DH24	OAKLEY_GROUP_DH24	24

DH组编号便是我们在配置IPSec参数时，指定的DH的值，如DH1,DH2,DH14,…。

DH算法交换原理可以用下图来说明：

不同DH组之间的根本区别在于选用的大素数不同。

而图中的p便是我们所说的大素数。我们通过指定DH组从而确定双方采用的大素数p的值。由于p本来就是公开的，可以在互联网上传输，因此即使公开协商DH组，即大素数p的值，也不存在安全性问题。

下面对openswan源码中DH密钥交换操作如何确定各个数值做一个简单介绍。

3. DH组对应的素数：

在源码实现中通过init_crypto(void)接口，来将大素数与对应的DH组进行绑定。同时也将每一个DH组所使用的原根(上图中的g)唯一确定了下来，无需再次进行协商。

而大素数就是代码中MODPxxx_ooo定义的，定义位置在left_constants.h。如下所示：

DH组编号	素数宏	素数值
DH1	MODP768_MODULUS	"FFFFFFFF FFFFFFFF C90FDAA2 2168C234 C4C6628B 80DC1CD1 " \ "29024E08 8A67CC74 020BBEA6 3B139B22 514A0879 8E3404DD " \ "EF9519B3 CD3A431B 302B0A6D F25F1437 4FE1356D 6D51C245 " \ "E485B576 625E7EC6 F44C42E9 A63A3620 FFFFFFFF FFFFFFFF"
DH2	MODP1024_MODULUS	"FFFFFFFF FFFFFFFF C90FDAA2 2168C234 C4C6628B 80DC1CD1 " \ "29024E08 8A67CC74 020BBEA6 3B139B22 514A0879 8E3404DD " \ "EF9519B3 CD3A431B 302B0A6D F25F1437 4FE1356D 6D51C245 " \ "E485B576 625E7EC6 F44C42E9 A637ED6B 0BFF5CB6 F406B7ED " \ "EE386BFB 5A899FA5 AE9F2411 7C4B1FE6 49286651 ECE65381 " \ "FFFFFFFF FFFFFFFF"
DH3	OAKLEY_GROUP_GP155
DH4	OAKLEY_GROUP_GP185
DH5	MODP1536_MODULUS	"FFFFFFFF FFFFFFFF C90FDAA2 2168C234 C4C6628B 80DC1CD1 " \ "29024E08 8A67CC74 020BBEA6 3B139B22 514A0879 8E3404DD " \ "EF9519B3 CD3A431B 302B0A6D F25F1437 4FE1356D 6D51C245 " \ "E485B576 625E7EC6 F44C42E9 A637ED6B 0BFF5CB6 F406B7ED " \ "EE386BFB 5A899FA5 AE9F2411 7C4B1FE6 49286651 ECE45B3D " \ "C2007CB8 A163BF05 98DA4836 1C55D39A 69163FA8 FD24CF5F " \ "83655D23 DCA3AD96 1C62F356 208552BB 9ED52907 7096966D " \ "670C354E 4ABC9804 F1746C08 CA237327 FFFFFFFF FFFFFFFF "
DH14	MODP2048_MODULUS	"FFFFFFFF FFFFFFFF C90FDAA2 2168C234 C4C6628B 80DC1CD1" \ "29024E08 8A67CC74 020BBEA6 3B139B22 514A0879 8E3404DD" \ "EF9519B3 CD3A431B 302B0A6D F25F1437 4FE1356D 6D51C245" \ "E485B576 625E7EC6 F44C42E9 A637ED6B 0BFF5CB6 F406B7ED" \ "EE386BFB 5A899FA5 AE9F2411 7C4B1FE6 49286651 ECE45B3D" \ "C2007CB8 A163BF05 98DA4836 1C55D39A 69163FA8 FD24CF5F" \ "83655D23 DCA3AD96 1C62F356 208552BB 9ED52907 7096966D" \ "670C354E 4ABC9804 F1746C08 CA18217C 32905E46 2E36CE3B" \ "E39E772C 180E8603 9B2783A2 EC07A28F B5C55DF0 6F4C52C9" \ "DE2BCBF6 95581718 3995497C EA956AE5 15D22618 98FA0510" \ "15728E5A 8AACAA68 FFFFFFFF FFFFFFFF"
DH15	MODP3072_MODULUS	"FFFFFFFF FFFFFFFF C90FDAA2 2168C234 C4C6628B 80DC1CD1" \ "29024E08 8A67CC74 020BBEA6 3B139B22 514A0879 8E3404DD" \ "EF9519B3 CD3A431B 302B0A6D F25F1437 4FE1356D 6D51C245" \ "E485B576 625E7EC6 F44C42E9 A637ED6B 0BFF5CB6 F406B7ED" \ "EE386BFB 5A899FA5 AE9F2411 7C4B1FE6 49286651 ECE45B3D" \ "C2007CB8 A163BF05 98DA4836 1C55D39A 69163FA8 FD24CF5F" \ "83655D23 DCA3AD96 1C62F356 208552BB 9ED52907 7096966D" \ "670C354E 4ABC9804 F1746C08 CA18217C 32905E46 2E36CE3B" \ "E39E772C 180E8603 9B2783A2 EC07A28F B5C55DF0 6F4C52C9" \ "DE2BCBF6 95581718 3995497C EA956AE5 15D22618 98FA0510" \ "15728E5A 8AAAC42D AD33170D 04507A33 A85521AB DF1CBA64" \ "ECFB8504 58DBEF0A 8AEA7157 5D060C7D B3970F85 A6E1E4C7" \ "ABF5AE8C DB0933D7 1E8C94E0 4A25619D CEE3D226 1AD2EE6B" \ "F12FFA06 D98A0864 D8760273 3EC86A64 521F2B18 177B200C" \ "BBE11757 7A615D6C 770988C0 BAD946E2 08E24FA0 74E5AB31" \ "43DB5BFC E0FD108E 4B82D120 A93AD2CA FFFFFFFF FFFFFFFF"
DH16	MODP4096_MODULUS	"FFFFFFFF FFFFFFFF C90FDAA2 2168C234 C4C6628B 80DC1CD1" \ "29024E08 8A67CC74 020BBEA6 3B139B22 514A0879 8E3404DD" \ "EF9519B3 CD3A431B 302B0A6D F25F1437 4FE1356D 6D51C245" \ "E485B576 625E7EC6 F44C42E9 A637ED6B 0BFF5CB6 F406B7ED" \ "EE386BFB 5A899FA5 AE9F2411 7C4B1FE6 49286651 ECE45B3D" \ "C2007CB8 A163BF05 98DA4836 1C55D39A 69163FA8 FD24CF5F" \ "83655D23 DCA3AD96 1C62F356 208552BB 9ED52907 7096966D" \ "670C354E 4ABC9804 F1746C08 CA18217C 32905E46 2E36CE3B" \ "E39E772C 180E8603 9B2783A2 EC07A28F B5C55DF0 6F4C52C9" \ "DE2BCBF6 95581718 3995497C EA956AE5 15D22618 98FA0510" \ "15728E5A 8AAAC42D AD33170D 04507A33 A85521AB DF1CBA64" \ "ECFB8504 58DBEF0A 8AEA7157 5D060C7D B3970F85 A6E1E4C7" \ "ABF5AE8C DB0933D7 1E8C94E0 4A25619D CEE3D226 1AD2EE6B" \ "F12FFA06 D98A0864 D8760273 3EC86A64 521F2B18 177B200C" \ "BBE11757 7A615D6C 770988C0 BAD946E2 08E24FA0 74E5AB31" \ "43DB5BFC E0FD108E 4B82D120 A9210801 1A723C12 A787E6D7" \ "88719A10 BDBA5B26 99C32718 6AF4E23C 1A946834 B6150BDA" \ "2583E9CA 2AD44CE8 DBBBC2DB 04DE8EF9 2E8EFC14 1FBECAA6" \ "287C5947 4E6BC05D 99B2964F A090C3A2 233BA186 515BE7ED" \ "1F612970 CEE2D7AF B81BDD76 2170481C D0069127 D5B05AA9" \ "93B4EA98 8D8FDDC1 86FFB7DC 90A6C08F 4DF435C9 34063199" \ "FFFFFFFF FFFFFFFF"
DH17	MODP6144_MODULUS	"FFFFFFFF FFFFFFFF C90FDAA2 2168C234 C4C6628B 80DC1CD1 29024E08" \ "8A67CC74 020BBEA6 3B139B22 514A0879 8E3404DD EF9519B3 CD3A431B" \ "302B0A6D F25F1437 4FE1356D 6D51C245 E485B576 625E7EC6 F44C42E9" \ "A637ED6B 0BFF5CB6 F406B7ED EE386BFB 5A899FA5 AE9F2411 7C4B1FE6" \ "49286651 ECE45B3D C2007CB8 A163BF05 98DA4836 1C55D39A 69163FA8" \ "FD24CF5F 83655D23 DCA3AD96 1C62F356 208552BB 9ED52907 7096966D" \ "670C354E 4ABC9804 F1746C08 CA18217C 32905E46 2E36CE3B E39E772C" \ "180E8603 9B2783A2 EC07A28F B5C55DF0 6F4C52C9 DE2BCBF6 95581718" \ "3995497C EA956AE5 15D22618 98FA0510 15728E5A 8AAAC42D AD33170D" \ "04507A33 A85521AB DF1CBA64 ECFB8504 58DBEF0A 8AEA7157 5D060C7D" \ "B3970F85 A6E1E4C7 ABF5AE8C DB0933D7 1E8C94E0 4A25619D CEE3D226" \ "1AD2EE6B F12FFA06 D98A0864 D8760273 3EC86A64 521F2B18 177B200C" \ "BBE11757 7A615D6C 770988C0 BAD946E2 08E24FA0 74E5AB31 43DB5BFC" \ "E0FD108E 4B82D120 A9210801 1A723C12 A787E6D7 88719A10 BDBA5B26" \ "99C32718 6AF4E23C 1A946834 B6150BDA 2583E9CA 2AD44CE8 DBBBC2DB" \ "04DE8EF9 2E8EFC14 1FBECAA6 287C5947 4E6BC05D 99B2964F A090C3A2" \ "233BA186 515BE7ED 1F612970 CEE2D7AF B81BDD76 2170481C D0069127" \ "D5B05AA9 93B4EA98 8D8FDDC1 86FFB7DC 90A6C08F 4DF435C9 34028492" \ "36C3FAB4 D27C7026 C1D4DCB2 602646DE C9751E76 3DBA37BD F8FF9406" \ "AD9E530E E5DB382F 413001AE B06A53ED 9027D831 179727B0 865A8918" \ "DA3EDBEB CF9B14ED 44CE6CBA CED4BB1B DB7F1447 E6CC254B 33205151" "2BD7AF42 6FB8F401 378CD2BF 5983CA01 C64B92EC F032EA15 D1721D03" \ "F482D7CE 6E74FEF6 D55E702F 46980C82 B5A84031 900B1C9E 59E7C97F" \ "BEC7E8F3 23A97A7E 36CC88BE 0F1D45B7 FF585AC5 4BD407B2 2B4154AA" \ "CC8F6D7E BF48E1D8 14CC5ED2 0F8037E0 A79715EE F29BE328 06A1D58B" \ "B7C5DA76 F550AA3D 8A1FBFF0 EB19CCB1 A313D55C DA56C9EC 2EF29632" \ "387FE8D7 6E3C0468 043E8F66 3F4860EE 12BF2D5B 0B7474D6 E694F91E" \ "6DCC4024 FFFFFFFF FFFFFFFF"
DH18	MODP8192_MODULUS	"FFFFFFFF FFFFFFFF C90FDAA2 2168C234 C4C6628B 80DC1CD1" \ "29024E08 8A67CC74 020BBEA6 3B139B22 514A0879 8E3404DD" \ "EF9519B3 CD3A431B 302B0A6D F25F1437 4FE1356D 6D51C245" \ "E485B576 625E7EC6 F44C42E9 A637ED6B 0BFF5CB6 F406B7ED" \ "EE386BFB 5A899FA5 AE9F2411 7C4B1FE6 49286651 ECE45B3D" \ "C2007CB8 A163BF05 98DA4836 1C55D39A 69163FA8 FD24CF5F" \ "83655D23 DCA3AD96 1C62F356 208552BB 9ED52907 7096966D" \ "670C354E 4ABC9804 F1746C08 CA18217C 32905E46 2E36CE3B" \ "E39E772C 180E8603 9B2783A2 EC07A28F B5C55DF0 6F4C52C9" \ "DE2BCBF6 95581718 3995497C EA956AE5 15D22618 98FA0510" \ "15728E5A 8AAAC42D AD33170D 04507A33 A85521AB DF1CBA64" \ "ECFB8504 58DBEF0A 8AEA7157 5D060C7D B3970F85 A6E1E4C7" \ "ABF5AE8C DB0933D7 1E8C94E0 4A25619D CEE3D226 1AD2EE6B" \ "F12FFA06 D98A0864 D8760273 3EC86A64 521F2B18 177B200C" \ "BBE11757 7A615D6C 770988C0 BAD946E2 08E24FA0 74E5AB31" \ "43DB5BFC E0FD108E 4B82D120 A9210801 1A723C12 A787E6D7" \ "88719A10 BDBA5B26 99C32718 6AF4E23C 1A946834 B6150BDA" \ "2583E9CA 2AD44CE8 DBBBC2DB 04DE8EF9 2E8EFC14 1FBECAA6" \ "287C5947 4E6BC05D 99B2964F A090C3A2 233BA186 515BE7ED" \ "1F612970 CEE2D7AF B81BDD76 2170481C D0069127 D5B05AA9" \ "93B4EA98 8D8FDDC1 86FFB7DC 90A6C08F 4DF435C9 34028492" \ "36C3FAB4 D27C7026 C1D4DCB2 602646DE C9751E76 3DBA37BD" \ "F8FF9406 AD9E530E E5DB382F 413001AE B06A53ED 9027D831" \ "179727B0 865A8918 DA3EDBEB CF9B14ED 44CE6CBA CED4BB1B" \ "DB7F1447 E6CC254B 33205151 2BD7AF42 6FB8F401 378CD2BF" \ "5983CA01 C64B92EC F032EA15 D1721D03 F482D7CE 6E74FEF6" \ "D55E702F 46980C82 B5A84031 900B1C9E 59E7C97F BEC7E8F3" \ "23A97A7E 36CC88BE 0F1D45B7 FF585AC5 4BD407B2 2B4154AA" \ "CC8F6D7E BF48E1D8 14CC5ED2 0F8037E0 A79715EE F29BE328" \ "06A1D58B B7C5DA76 F550AA3D 8A1FBFF0 EB19CCB1 A313D55C" \ "DA56C9EC 2EF29632 387FE8D7 6E3C0468 043E8F66 3F4860EE" \ "12BF2D5B 0B7474D6 E694F91E 6DBE1159 74A3926F 12FEE5E4" \ "38777CB6 A932DF8C D8BEC4D0 73B931BA 3BC832B6 8D9DD300" \ "741FA7BF 8AFC47ED 2576F693 6BA42466 3AAB639C 5AE4F568" \ "3423B474 2BF1C978 238F16CB E39D652D E3FDB8BE FC848AD9" \ "22222E04 A4037C07 13EB57A8 1A23F0C7 3473FC64 6CEA306B" \ "4BCBC886 2F8385DD FA9D4B7F A2C087E8 79683303 ED5BDD3A" \ "062B3CF5 B3A278A6 6D2A13F8 3F44F82D DF310EE0 74AB6A36" \ "4597E899 A0255DC1 64F31CC5 0846851D F9AB4819 5DED7EA1" \ "B1D510BD 7EE74D73 FAF36BC3 1ECFA268 359046F4 EB879F92" \ "4009438B 481C6CD7 889A002E D5EE382B C9190DA6 FC026E47" \ "9558E447 5677E9AA 9E3050E2 765694DF C81F56E8 80B96E71" \ "60C980DD 98EDD3DF FFFFFFFF FFFFFFFF"
DH22	OAKLEY_GROUP_DH22	"B10B8F96 A080E01D DE92DE5E AE5D54EC 52C99FBC FB06A3C6 " \ "9A6A9DCA 52D23B61 6073E286 75A23D18 9838EF1E 2EE652C0 " \ "13ECB4AE A9061123 24975C3C D49B83BF ACCBDD7D 90C4BD70 " \ "98488E9C 219A7372 4EFFD6FA E5644738 FAA31A4F F55BCCC0 " \ "A151AF5F 0DC8B4BD 45BF37DF 365C1A65 E68CFDA7 6D4DA708 " \ "DF1FB2BC 2E4A4371"
DH23	OAKLEY_GROUP_DH23	"AD107E1E 9123A9D0 D660FAA7 9559C51F A20D64E5 683B9FD1 " \ "B54B1597 B61D0A75 E6FA141D F95A56DB AF9A3C40 7BA1DF15 " \ "EB3D688A 309C180E 1DE6B85A 1274A0A6 6D3F8152 AD6AC212 " \ "9037C9ED EFDA4DF8 D91E8FEF 55B7394B 7AD5B7D0 B6C12207 " \ "C9F98D11 ED34DBF6 C6BA0B2C 8BBC27BE 6A00E0A0 B9C49708 " \ "B3BF8A31 70918836 81286130 BC8985DB 1602E714 415D9330 " \ "278273C7 DE31EFDC 7310F712 1FD5A074 15987D9A DC0A486D " \ "CDF93ACC 44328387 315D75E1 98C641A4 80CD86A1 B9E587E8 " \ "BE60E69C C928B2B9 C52172E4 13042E9B 23F10B0E 16E79763 " \ "C9B53DCF 4BA80A29 E3FB73C1 6B8E75B9 7EF363E2 FFA31F71 " \ "CF9DE538 4E71B81C 0AC4DFFE 0C10E64F"
DH24	OAKLEY_GROUP_DH24	"87A8E61D B4B6663C FFBBD19C 65195999 8CEEF608 660DD0F2 " \ "5D2CEED4 435E3B00 E00DF8F1 D61957D4 FAF7DF45 61B2AA30 " \ "16C3D911 34096FAA 3BF4296D 830E9A7C 209E0C64 97517ABD " \ "5A8A9D30 6BCF67ED 91F9E672 5B4758C0 22E0B1EF 4275BF7B " \ "6C5BFC11 D45F9088 B941F54E B1E59BB8 BC39A0BF 12307F5C " \ "4FDB70C5 81B23F76 B63ACAE1 CAA6B790 2D525267 35488A0E " \ "F13C6D9A 51BFA4AB 3AD83477 96524D8E F6A167B5 A41825D9 " \ "67E144E5 14056425 1CCACB83 E6B486F6 B3CA3F79 71506026 " \ "C0B857F6 89962856 DED4010A BD0BE621 C3A3960A 54E710C3 " \ "75F26375 D7014103 A4B54330 C198AF12 6116D227 6E11715F " \ "693877FA D7EF09CA DB094AE9 1E1A1597"

4. DH组选用的原根：

任意质数p都一定存在原根g

上面这句话就是一个定理，将其记住就行，如果需要证明，据说需要数论中的拉格朗日定理和欧拉函数。这里需要说明的是：每一个质数可能存在多个原根，而DH密钥交换时选用哪个原根变成了疑问。实际上由于该值可以公开传输，因此并不存在问题，但是在IKE协商过程中并没有传输该值，因此在阅读openswan源码中发现，DH组与原根是一一绑定的，当我们确定了DH组后，选用的原根便已经确定。代码实现同样是在init_crypto中：

整理成表格如下：

生成元对象	说明	生成元(原根)
MODP_GENERATOR	它是DH1, DH2, DH5, DH14, DH15, DH16, DH17, DH18的原根	"2"
MODP_GENERATOR_DH22	它是DH22的原根	"A4D1CBD5 C3FD3412 6765A442 EFB99905 F8104DD2 58AC507F " \ "D6406CFF 14266D31 266FEA1E 5C41564B 777E690F 5504F213 " \ "160217B4 B01B886A 5E91547F 9E2749F4 D7FBD7D3 B9A92EE1 " \ "909D0D22 63F80A76 A6A24C08 7A091F53 1DBF0A01 69B6A28A " \ "D662A4D1 8E73AFA3 2D779D59 18D08BC8 858F4DCE F97C2A24 " \ "855E6EEB 22B3B2E5"
MODP_GENERATOR_DH23	它是DH23的原根	"AC4032EF 4F2D9AE3 9DF30B5C 8FFDAC50 6CDEBE7B 89998CAF " \ "74866A08 CFE4FFE3 A6824A4E 10B9A6F0 DD921F01 A70C4AFA " \ "AB739D77 00C29F52 C57DB17C 620A8652 BE5E9001 A8D66AD7 " \ "C1766910 1999024A F4D02727 5AC1348B B8A762D0 521BC98A " \ "E2471504 22EA1ED4 09939D54 DA7460CD B5F6C6B2 50717CBE " \ "F180EB34 118E98D1 19529A45 D6F83456 6E3025E3 16A330EF " \ "BB77A86F 0C1AB15B 051AE3D4 28C8F8AC B70A8137 150B8EEB " \ "10E183ED D19963DD D9E263E4 770589EF 6AA21E7F 5F2FF381 " \ "B539CCE3 409D13CD 566AFBB4 8D6C0191 81E1BCFE 94B30269 " \ "EDFE72FE 9B6AA4BD 7B5A0F1C 71CFFF4C 19C418E1 F6EC0179 " \ "81BC087F 2A7065B3 84B890D3 191F2BFA"
MODP_GENERATOR_DH24	它是DH24的原根	"3FB32C9B 73134D0B 2E775066 60EDBD48 4CA7B18F 21EF2054 " \ "07F4793A 1A0BA125 10DBC150 77BE463F FF4FED4A AC0BB555 " \ "BE3A6C1B 0C6B47B1 BC3773BF 7E8C6F62 901228F8 C28CBB18 " \ "A55AE313 41000A65 0196F931 C77A57F2 DDF463E5 E9EC144B " \ "777DE62A AAB8A862 8AC376D2 82D6ED38 64E67982 428EBC83 " \ "1D14348F 6F2F9193 B5045AF2 767164E1 DFC967C1 FB3F2E55 " \ "A4BD1BFF E83B9C80 D052B985 D182EA0A DB2A3B73 13D3FE14 " \ "C8484B1E 052588B9 B7D2BBD2 DF016199 ECD06E15 57CD0915 " \ "B3353BBB 64E0EC37 7FD02837 0DF92B52 C7891428 CDC67EB6 " \ "184B523D 1DB246C3 2F630784 90F00EF8 D647D148 D4795451 " \ "5E2327CF EF98C582 664B4C0F 6CC41659"