ssh - no matching key exchange method found

建议

遇到类似问题不要限于解决当前问题，举一反三、深入理解

例如错误提示具体什么意思，连接过程是怎样，更进一步”对称、非对称、hash 常见算法，试用场景”等

现象

ssh客户端连接服务端失败

错误信息示例

test@dev ~ $ ssh test@192.168.0.100
Unable to negotiate with 192.168.0.100 port 22: no matching key exchange method found. Their offer: diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha1,diffie-hellman-group1-sha1

更多详情可追加-vv，一些关键信息如下

debug2: local client KEXINIT proposal
debug2: KEX algorithms: curve25519-sha256,curve25519-sha256@libssh.org,ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group16-sha512,diffie-hellman-group18-sha512,diffie-hellman-group14-sha256,ext-info-c
debug2: host key algorithms: rsa-sha2-512-cert-v01@openssh.com,rsa-sha2-256-cert-v01@openssh.com,ssh-rsa-cert-v01@openssh.com,rsa-sha2-512,rsa-sha2-256,ssh-rsa,ssh-ed25519-cert-v01@openssh.com,ecdsa-sha2-nistp256-cert-v01@openssh.com,ecdsa-sha2-nistp384-cert-v01@openssh.com,ecdsa-sha2-nistp521-cert-v01@openssh.com,sk-ssh-ed25519-cert-v01@openssh.com,sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,ssh-ed25519,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,sk-ssh-ed25519@openssh.com,sk-ecdsa-sha2-nistp256@openssh.com
debug2: ciphers ctos: chacha20-poly1305@openssh.com,aes128-ctr,aes192-ctr,aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com
debug2: ciphers stoc: chacha20-poly1305@openssh.com,aes128-ctr,aes192-ctr,aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com
debug2: MACs ctos: umac-64-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,hmac-sha1-etm@openssh.com,umac-64@openssh.com,umac-128@openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-sha1
debug2: MACs stoc: umac-64-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,hmac-sha1-etm@openssh.com,umac-64@openssh.com,umac-128@openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-sha1
debug2: compression ctos: none,zlib@openssh.com,zlib
debug2: compression stoc: none,zlib@openssh.com,zlib
debug2: languages ctos:
debug2: languages stoc:
debug2: first_kex_follows 0
debug2: reserved 0
debug2: peer server KEXINIT proposal
debug2: KEX algorithms: diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha1,diffie-hellman-group1-sha1
debug2: host key algorithms: ssh-rsa
debug2: ciphers ctos: aes128-cbc,3des-cbc,des-cbc
debug2: ciphers stoc: aes128-cbc,3des-cbc,des-cbc
debug2: MACs ctos: hmac-sha1,hmac-sha1-96,hmac-md5,hmac-md5-96
debug2: MACs stoc: hmac-sha1,hmac-sha1-96,hmac-md5,hmac-md5-96
debug2: compression ctos: none
debug2: compression stoc: none

原因

出现这种情况一般是客户端/服务端因为软件版本差异或经过裁剪等原因导致的默认支持的算法不同造成的

从debug信息里也可以看到，连接过程中客户端/服务端涉及以下几个方面的协商:

• KEX（Key Exchange）

  密钥交换算法协商，一般是非对称算法：安全性高、性能低

  ssh -Q kex 罗列支持的算法

• ciphers

  加密算法，一般是对称算法：相对安全性低、性能高

  ssh -Q cipher 罗列支持的算法

• MACs

  MAC（message authentication code），数据完整性校验用，一般是hash算法（单向）

  ssh -Q mac 罗列支持的算法

• compression

  是否启用压缩

解决方式

选用双方都支持的算法，例如

~/.ssh/config

Host 192.168.0.100
    KexAlgorithms +diffie-hellman-group1-sha1
    Ciphers +aes128-cbc

更多man ssh_config