70 lines
1.7 KiB
Bash
70 lines
1.7 KiB
Bash
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#!/bin/bash -e
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# Parse the data directory of a PE/COFF file and returns two hex values:
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# the file offset and size of the signature table.
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function sigtable_params() {
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filename="$1"
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objdump -p "$filename" | awk '/^Entry 4/ {print "0x"$3 " " "0x"$4}'
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}
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# Extract the signature from a file containing a signature table,
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# and write to stdout
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function extract_sig() {
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filename="$1"
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cert_table_header_size=8
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params=($(hexdump -n$cert_table_header_size \
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-e '/4 "%u " /2 "%04x " /2 "%04x\n"' \
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"$filename"))
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cert_size=${params[0]}
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cert_revision=${params[1]}
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cert_type=${params[2]}
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# check type & revision
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[ "$cert_revision" -eq '0200' ]
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[ "$cert_type" -eq '0002' ]
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dd if="$filename" bs=1 skip=$cert_table_header_size \
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count=$(($cert_size - $cert_table_header_size)) 2>/dev/null
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}
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function repeat() {
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str=$1
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count=$2
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for (( i = 0; $i < $count; i++ ))
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do
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echo -n "$str"
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done
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}
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cert="test.cert"
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signed="test.signed"
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for i in {1..8}
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do
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# generate a variable-length parameter for the certificate subject
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subj="/CN=$(repeat 'x' $i)"
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# create a temporary cert, and sign the image with it
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openssl req -x509 -sha256 -subj "$subj" -new -key "$key" -out "$cert"
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"$sbsign" --cert "$cert" --key "$key" --output "$signed" "$image"
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# extract the sigtable
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params=($(sigtable_params "$signed"))
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# split and convert to base-10
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sigtable_offset=$((${params[0]}))
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sigtable_size=$((${params[1]}))
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# check that we have a correctly-padded sigtable
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[ $(($sigtable_size % 8)) -eq 0 ]
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sigtable='test.sigtable'
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dd if="$signed" bs=1 skip=$sigtable_offset count=$sigtable_size \
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of=$sigtable 2>/dev/null
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# extract sig, and feed to openssl's PKCS7 parser
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extract_sig "$sigtable" | openssl pkcs7 -inform DER -noout
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done
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