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sslgetcert: Add EC Point Formats extension to TLS handshake (fix connections to Vercel servers) #15

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sslgetcert: Add EC Point Formats extension to TLS handshake (fix connections to Vercel servers) #15

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47 changes: 46 additions & 1 deletion eperd/sslgetcert.c
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Original file line number Diff line number Diff line change
Expand Up @@ -611,6 +611,29 @@ static void add_compression(struct hsbuf *hsbuf)
hsbuf_add(hsbuf, compression, len);
}

static void ext_ec_point_formats(struct hsbuf *hsbuf)
{
/*
The EC Point Format extension contains one octet of length,
followed by a series of one-octet values of entries in the
EC Point Format registry.
*/
uint16_t epfextlen;
uint8_t epflen;
size_t len;
uint8_t point_formats[]= { 0x0 /* uncompressed */ };

len = sizeof(point_formats);

epflen = len;
epfextlen = 1 + len;

hsbuf_add_u16(hsbuf, 11 /*ec_point_formats*/);
hsbuf_add_u16(hsbuf, epfextlen);
hsbuf_add(hsbuf, &epflen, sizeof(epflen));
hsbuf_add(hsbuf, point_formats, len);
}

static void ext_sigs(struct hsbuf *hsbuf)
{
uint16_t sigextlen, siglen;
Expand Down Expand Up @@ -682,18 +705,32 @@ static void sni(struct hsbuf *hsbuf, const char *server_name)
hsbuf_add(hsbuf, server_name, size_hostname);
}

/* Only add EC point format extension for TLS versions 1.0, 1.1, and 1.2 */
static int ec_point_ext_ok(const struct state *state) {
return (state->major_version == 3) &&
(state->minor_version >= 1) &&
(state->minor_version <= 3);
}

static void add_extensions(struct state *state, struct hsbuf *hsbuf)
{
size_t size_extensions;
struct hsbuf ext_sigs_buf;
struct hsbuf sni_buf;
struct hsbuf ec_point_formats_buf;
struct hsbuf elliptic_curves_buf;

/* SNI */
hsbuf_init(&sni_buf);
if (state->sni)
sni(&sni_buf, state->sni);

/* EC point format */
if (ec_point_ext_ok(state)) {
hsbuf_init(&ec_point_formats_buf);
ext_ec_point_formats(&ec_point_formats_buf);
}

/* Signatures */
hsbuf_init(&ext_sigs_buf);
ext_sigs(&ext_sigs_buf);
Expand All @@ -702,12 +739,20 @@ static void add_extensions(struct state *state, struct hsbuf *hsbuf)
hsbuf_init(&elliptic_curves_buf);
elliptic_curves(&elliptic_curves_buf);

size_extensions= hsbuf_len(&sni_buf) + hsbuf_len(&ext_sigs_buf) +
size_extensions= hsbuf_len(&sni_buf) +
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If statement applies here too.

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@dkg this comment will need fixing.

hsbuf_len(&ext_sigs_buf) +
hsbuf_len(&elliptic_curves_buf);

if (ec_point_ext_ok(state))
size_extensions += hsbuf_len(&ec_point_formats_buf);

hsbuf_add_u16(hsbuf, size_extensions);
hsbuf_copy(hsbuf, &sni_buf);
hsbuf_cleanup(&sni_buf);
if (ec_point_ext_ok(state)) {
hsbuf_copy(hsbuf, &ec_point_formats_buf);
hsbuf_cleanup(&ec_point_formats_buf);
}
hsbuf_copy(hsbuf, &ext_sigs_buf);
hsbuf_cleanup(&ext_sigs_buf);
hsbuf_copy(hsbuf, &elliptic_curves_buf);
Expand Down