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annotate sk-ecdsa.c @ 1928:333688ec53d0

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Handle ecdsa-sk flags, reject no-touch For the time being Dropbear will only allow SK auth with default parameters, user-presence needs to be set. In future handling of authorized_keys option "no-touch-required" can be added. This code would also be refactored to share between ecdsa and ed25519 once I get hardware/emulation to test ed25519.
author Matt Johnston <matt@ucc.asn.au>
date Wed, 30 Mar 2022 21:06:15 +0800
parents 35d504d59c05
children
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1 #include "includes.h"
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3 #if DROPBEAR_SK_ECDSA
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5 #include "dbutil.h"
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6 #include "ecc.h"
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7 #include "ecdsa.h"
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8 #include "sk-ecdsa.h"
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9 #include "ssh.h"
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11 int buf_sk_ecdsa_verify(buffer *buf, const ecc_key *key, const buffer *data_buf, const char* app, unsigned int applen) {
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12 hash_state hs;
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13 unsigned char subhash[SHA256_HASH_SIZE];
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14 buffer *sk_buffer = NULL, *sig_buffer = NULL;
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15 unsigned char flags;
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16 unsigned int counter;
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17 int ret;
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19 TRACE(("buf_sk_ecdsa_verify"))
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21 /* from https://github.com/openssh/openssh-portable/blob/master/PROTOCOL.u2f */
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22 /* ecdsa signature to verify (r, s) */
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23 sig_buffer = buf_getbuf(buf);
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25 flags = buf_getbyte (buf);
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26 counter = buf_getint (buf);
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27 /* create the message to be signed */
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28 sk_buffer = buf_new (2*SHA256_HASH_SIZE+5);
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29 sha256_init (&hs);
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30 sha256_process (&hs, app, applen);
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31 sha256_done (&hs, subhash);
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32 buf_putbytes (sk_buffer, subhash, sizeof (subhash));
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33 buf_putbyte (sk_buffer, flags);
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34 buf_putint (sk_buffer, counter);
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35 sha256_init (&hs);
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36 sha256_process (&hs, data_buf->data, data_buf->len);
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37 sha256_done (&hs, subhash);
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38 buf_putbytes (sk_buffer, subhash, sizeof (subhash));
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40 ret = buf_ecdsa_verify(sig_buffer, key, sk_buffer);
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41 buf_free(sk_buffer);
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42 buf_free(sig_buffer);
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44 /* TODO: allow "no-touch-required" or "verify-required" authorized_keys options */
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45 if (!(flags & SSH_SK_USER_PRESENCE_REQD)) {
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46 if (ret == DROPBEAR_SUCCESS) {
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47 dropbear_log(LOG_WARNING, "Rejecting, user-presence not set");
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48 }
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49 ret = DROPBEAR_FAILURE;
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50 }
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51
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52 TRACE(("leave buf_sk_ecdsa_verify, ret=%d", ret))
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53 return ret;
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54 }
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56 #endif /* DROPBEAR_SK_ECDSA */