问题描述
我正在尝试在我的 IoT 项目中实施 SSL 客户端。我已将在 STM32Cube_FW_F7_V1.15.0 中找到的 SSL_Client 示例复制到我的项目中，并且能够成功编译。但是 SSL 握手失败并显示 -0x7780 MbedTLS_ERR_SSL_FATAL_ALERT_MESSAGE。我附上控制台调试输出：
. seeding the random number generator... ok
. Loading the CA root certificate ... ok (1 skipped)
. Connecting to tcp/www.google.de/443... ok
. Setting up the SSL/TLS structure... ok
. Performing the SSL/TLS handshake...=> handshake
client state: 0
=> flush output
<= flush output
client state: 1
=> flush output
<= flush output
=> write client hello
client hello,max version: [3:3]
dumping 'client hello,random bytes' (32 bytes)
0000: e2 13 bf 6d 61 b6 fb a6 82 a4 59 f0 0b ef e9 03 ...ma.....Y.....
0010: 44 be de 3c 49 3d 39 56 51 60 3b b6 49 c4 17 50 D..<I=9VQ`;.I..P
client hello,session id len.: 0
dumping 'client hello,session id' (0 bytes)
client hello,add ciphersuite: c02b
client hello,got 1 ciphersuites (excluding SCSVs)
adding EMPTY_RENEGOTIATION_INFO_SCSV
client hello,compress len.: 1
client hello,compress alg.: 0
client hello,adding server name extension: www.google.de
client hello,adding signature_algorithms extension
client hello,adding supported_elliptic_curves extension
client hello,adding supported_point_formats extension
client hello,adding encrypt_then_mac extension
client hello,adding extended_master_secret extension
client hello,adding session ticket extension
client hello,total extension length: 62
=> write handshake message
=> write record
output record: msgtype = 22,version = [3:3],msglen = 111
dumping 'output record sent to network' (116 bytes)
0000: 16 03 03 00 6f 01 00 00 6b 03 03 e2 13 bf 6d 61 ....o...k.....ma
0010: b6 fb a6 82 a4 59 f0 0b ef e9 03 44 be de 3c 49 .....Y.....D..<I
0020: 3d 39 56 51 60 3b b6 49 c4 17 50 00 00 04 c0 2b =9VQ`;.I..P....+
0030: 00 ff 01 00 00 3e 00 00 00 12 00 10 00 00 0d 77 .....>.........w
0040: 77 77 2e 67 6f 6f 67 6c 65 2e 64 65 00 0d 00 0a ww.google.de....
0050: 00 08 04 03 04 01 03 03 03 01 00 0a 00 04 00 02 ................
0060: 00 15 00 0b 00 02 01 00 00 16 00 00 00 17 00 00 ................
0070: 00 23 00 00 .#..
=> flush output
message length: 116,out_left: 116
ssl->f_send() returned 116 (-0xffffff8c)
<= flush output
<= write record
<= write handshake message
<= write client hello
client state: 2
=> flush output
<= flush output
=> parse server hello
=> read record
=> fetch input
in_left: 0,nb_want: 5
in_left: 0,nb_want: 5
ssl->f_recv(_timeout)() returned 5 (-0xfffffffb)
<= fetch input
dumping 'input record header' (5 bytes)
0000: 15 03 03 00 02 .....
input record: msgtype = 21,msglen = 2
=> fetch input
in_left: 5,nb_want: 7
in_left: 5,nb_want: 7
ssl->f_recv(_timeout)() returned 2 (-0xfffffffe)
<= fetch input
dumping 'input record from network' (7 bytes)
0000: 15 03 03 00 02 02 28 ......(
got an alert message,type: [2:40]
is a fatal alert message (msg 40)
mbedtls_ssl_handle_message_type() returned -30592 (-0x7780)
mbedtls_ssl_read_record() returned -30592 (-0x7780)
ERR
<= handshake
Failed
! mbedtls_ssl_handshake returned -0x7780
非常感谢任何帮助！
更新：
问题是密钥交换方法。只有 MbedTLS_KEY_EXCHANGE_ECDHE_ECDSA_ENABLED 处于活动状态。在我添加 MbedTLS_KEY_EXCHANGE_ECDHE_RSA_ENABLED（以及所需的 MbedTLS_RSA_C、MbedTLS_PKCS1_V21 和 MbedTLS_PKCS1_V15）之后，握手发生了。非常感谢您为我指出正确的方向吉尔斯
解决方法
连接失败，因为服务器在收到第一个 TLS 消息（ClientHello）后立即决定关闭连接。它发送 alert 40，这是“握手失败”。不幸的是，这是一个笼统的“我不喜欢我听到的，我不能和你说话”，它没有提供任何关于它不喜欢什么的信息。您的 TLS 客户端有问题，或者很可能是配置错误并发送了 Google 服务器不接受的内容。
Wireshark 有助于诊断网络协议问题。让我们看看它对您的客户端发送的数据有何看法。我不是 Wireshark 专家，所以我是通过手动方式完成的，方法是启动 Wireshark，告诉它监听 port 443 && host www.google.de 并使用
<clienthello.hex xxd -r -p | socket www.google.de 443 | xxd -p
这是 Wireshark 提供的 ClientHello 的转储：
TLSv1.2 Record Layer: Handshake Protocol: Client Hello
Content Type: Handshake (22)
Version: TLS 1.2 (0x0303)
Length: 111
Handshake Protocol: Client Hello
Handshake Type: Client Hello (1)
Length: 107
Version: TLS 1.2 (0x0303)
Random: e213bf6d61b6fba682a459f00befe90344bede3c493d3956…
GMT Unix Time: Mar 11,2090 20:50:05.000000000 CET
Random Bytes: 61b6fba682a459f00befe90344bede3c493d395651603bb6…
Session ID Length: 0
Cipher Suites Length: 4
Cipher Suites (2 suites)
Cipher Suite: TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256 (0xc02b)
Cipher Suite: TLS_EMPTY_RENEGOTIATION_INFO_SCSV (0x00ff)
Compression Methods Length: 1
Compression Methods (1 method)
Compression Method: null (0)
Extensions Length: 62
Extension: server_name (len=18)
Type: server_name (0)
Length: 18
Server Name Indication extension
Server Name list length: 16
Server Name Type: host_name (0)
Server Name length: 13
Server Name: www.google.de
Extension: signature_algorithms (len=10)
Type: signature_algorithms (13)
Length: 10
Signature Hash Algorithms Length: 8
Signature Hash Algorithms (4 algorithms)
Signature Algorithm: ecdsa_secp256r1_sha256 (0x0403)
Signature Hash Algorithm Hash: SHA256 (4)
Signature Hash Algorithm Signature: ECDSA (3)
Signature Algorithm: rsa_pkcs1_sha256 (0x0401)
Signature Hash Algorithm Hash: SHA256 (4)
Signature Hash Algorithm Signature: RSA (1)
Signature Algorithm: SHA224 ECDSA (0x0303)
Signature Hash Algorithm Hash: SHA224 (3)
Signature Hash Algorithm Signature: ECDSA (3)
Signature Algorithm: SHA224 RSA (0x0301)
Signature Hash Algorithm Hash: SHA224 (3)
Signature Hash Algorithm Signature: RSA (1)
Extension: supported_groups (len=4)
Type: supported_groups (10)
Length: 4
Supported Groups List Length: 2
Supported Groups (1 group)
Supported Group: secp224r1 (0x0015)
Extension: ec_point_formats (len=2)
Type: ec_point_formats (11)
Length: 2
EC point formats Length: 1
Elliptic curves point formats (1)
EC point format: uncompressed (0)
Extension: encrypt_then_mac (len=0)
Type: encrypt_then_mac (22)
Length: 0
Extension: extended_master_secret (len=0)
Type: extended_master_secret (23)
Length: 0
Extension: session_ticket (len=0)
Type: session_ticket (35)
Length: 0
Data (0 bytes)
仔细看，除了这个之外，大部分内容都不足为奇：
Supported Groups (1 group)
Supported Group: secp224r1 (0x0015)
Secp224r1 是一种很少使用且官方已弃用的曲线。很少有服务器接受它。
重新配置 Mbed TLS 以支持 secp256r1。这是 ECDH+ECDSA 资源受限设备的实际标准曲线（ECDH+EdDSA 或 Curve25519+Ed25519）。在 mbedtls/config.h 中，不是列出 MBEDTLS_ECP_DP_SECP224R1_ENABLED，而是列出 MBEDTLS_ECP_DP_SECP256R1_ENABLED。如果您设置了 MBEDTLS_ECP_MAX_BITS，请确保将其设置为 256（或更多）。