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Add padding extension 

RFC 7685 notes that there is at least one TLS implementation that hangs if the client sends a ClientHello with a TLSCiphertext.length between 256 and 511 bytes, and so the padding extension was defined in order to get around this bug. (OpenSSL s_client includes this extension when the -bugs option is used.) So, I changed socksend_tls_clienthello() to include the padding extension if the CLientHello would have a length between 256 and 511 bytes, making the padding extension just large enough to make the ClientHello 512 bytes.

I also fixed a typo (a missing "0x") in the check for whether any ECC ciphers are included in the Client Hello.
This commit is contained in:
David Cooper 2016-05-03 16:48:42 -04:00
parent 7e506e5c5a
commit 120a5c86ef
1 changed files with 34 additions and 13 deletions
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47
testssl.sh
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@ -4170,13 +4170,13 @@ socksend_tls_clienthello() {
local servername_hexstr len_servername len_servername_hex
local hexdump_format_str part1 part2
local all_extensions=""
local -i i j len_extension
local len_sni_listlen len_sni_ext len_extension_hex
local -i i j len_extension len_padding_extension len_all
local len_sni_listlen len_sni_ext len_extension_hex len_padding_extension_hex
local cipher_suites len_ciph_suites len_ciph_suites_byte len_ciph_suites_word
local len_client_hello_word len_all_word
local ecc_cipher_suite_found=false
local extension_signature_algorithms extension_heartbeat
local extension_session_ticket extension_next_protocol extensions_ecc
local extension_session_ticket extension_next_protocol extensions_ecc extension_padding
code2network "$2" # convert CIPHER_SUITES
cipher_suites="$NW_STR" # we don't have the leading \x here so string length is two byte less, see next
@ -4184,6 +4184,12 @@ socksend_tls_clienthello() {
len_ciph_suites_byte=$(echo ${#cipher_suites})
let "len_ciph_suites_byte += 2"
# we have additional 2 chars \x in each 2 byte string and 2 byte ciphers, so we need to divide by 4:
len_ciph_suites=$(printf "%02x\n" $(($len_ciph_suites_byte / 4 )))
len2twobytes "$len_ciph_suites"
len_ciph_suites_word="$LEN_STR"
#[[ $DEBUG -ge 3 ]] && echo $len_ciph_suites_word
if [[ "$tls_low_byte" != "00" ]]; then
# Add extensions
@ -4211,7 +4217,7 @@ socksend_tls_clienthello() {
ecc_cipher_suite_found=true && break
fi
elif [[ "$part1" == "0xcc" ]]; then
if [[ "$part2" == "0xa8" ]] || [[ "$part2" == "0xa9" ]] || [[ "$part2" == "0xac" ]] || [[ "$part2" == "13" ]] || [[ "$part2" == "0x14" ]]; then
if [[ "$part2" == "0xa8" ]] || [[ "$part2" == "0xa9" ]] || [[ "$part2" == "0xac" ]] || [[ "$part2" == "0x13" ]] || [[ "$part2" == "0x14" ]]; then
ecc_cipher_suite_found=true && break
fi
fi
@ -4282,16 +4288,31 @@ socksend_tls_clienthello() {
len_extension+=2
len_extension=$len_extension/4
len_extension_hex=$(printf "%02x\n" $len_extension)
all_extensions="
,00, $len_extension_hex # first the len of all extentions.
,$all_extensions"
fi
# we have additional 2 chars \x in each 2 byte string and 2 byte ciphers, so we need to divide by 4:
len_ciph_suites=$(printf "%02x\n" $(($len_ciph_suites_byte / 4 )))
len2twobytes "$len_ciph_suites"
len_ciph_suites_word="$LEN_STR"
#[[ $DEBUG -ge 3 ]] && echo $len_ciph_suites_word
# If the length of the Client Hello would be between 256 and 511 bytes,
# then add a padding extension (see RFC 7685)
len_all=$((0x$len_ciph_suites + 0x2b + 0x$len_extension_hex + 0x2))
if [[ $len_all -ge 256 ]] && [[ $len_all -le 511 ]]; then
if [[ $len_all -gt 508 ]]; then
len_padding_extension=0
else
len_padding_extension=$((508 - 0x$len_ciph_suites - 0x2b - 0x$len_extension_hex - 0x2))
fi
len_padding_extension_hex=$(printf "%02x\n" $len_padding_extension)
len2twobytes "$len_padding_extension_hex"
all_extensions="$all_extensions\\x00\\x15\\x${LEN_STR:0:2}\\x${LEN_STR:4:2}"
for (( i=0; i<len_padding_extension; i++ )); do
all_extensions="$all_extensions\\x00"
done
len_extension=$len_extension+$len_padding_extension+0x4
len_extension_hex=$(printf "%02x\n" $len_extension)
fi
len2twobytes "$len_extension_hex"
all_extensions="
,$LEN_STR # first the len of all extentions.
,$all_extensions"
fi
# RFC 3546 doesn't specify SSLv3 to have SNI, openssl just ignores the switch if supplied
if [[ "$tls_low_byte" == "00" ]]; then