initial commit: header

* func to write the header APC NMC expects

.gitignore

@@ -0,0 +1,3 @@
+# key/cert files
+*.p15
+*.pem

file_header.go

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+package main
+
+import (
+	"encoding/binary"
+	"errors"
+
+	"github.com/sigurn/crc16"
+)
+
+// makeFileHeader generates the 228 byte header to prepend to the .p15
+// as required by APC UPS NMC. Only 2,048 bit RSA keys are supported
+// so the header will always be written with that key size assumption
+func makeFileHeader(p15File []byte) ([]byte, error) {
+	// original reference code from: https://github.com/bbczeuz/apc_tools
+	// // add APC header
+	// *(uint32_t *)(buf + 0) = 1; // always 1
+	// *(uint32_t *)(buf + 4) = 1; // always 1
+	// strncpy((char *)(buf + 8), "SecurityWizard103", 0xC8); // apparently supposed to identify the creating tool, SecWiz v1.04 sill puts 103 here
+	// *(uint32_t *)(buf + 208) = 1; // always 1
+	// *(uint32_t *)(buf + 212) = 1; // always 1
+	// *(uint32_t *)(buf + 216) = fileSize; // size of the following data
+	// *(uint32_t *)(buf + 208) = keySize; // 1 for 1024 key, otherwise (2048 bit) 2
+	// // 16 bit checksums are moved to 32 bit int with sign-extension
+	// *(uint32_t *)(buf + 220) = (int32_t)calc_cksum(0, buf + 228, fileSize); // checksum of the original file
+	// *(uint32_t *)(buf + 224) = (int32_t)calc_cksum(0, buf, 224); // checksum of the APC header
+
+	// NOTE: This line is unused as it seems the APC tool code always writes this as a 1 for 2,048 bit
+	// 		*(uint32_t *)(buf + 208) = keySize; // 1 for 1024 key, otherwise (2048 bit) 2
+	// Unsure why this was in original code but seems irrelevant
+
+	header := make([]byte, 228)
+
+	// always 1
+	header[0] = 1
+
+	// always 1
+	header[4] = 1
+
+	// apparently supposed to identify the creating tool
+	toolName := "NMCSecurityWizardCLI100"
+	toolNameBytes := []byte(toolName)
+	if len(toolNameBytes) > 200 {
+		return nil, errors.New("tool name is too big to fit in header")
+	}
+	copy(header[8:], toolNameBytes)
+
+	// always 1
+	header[208] = 1
+
+	// always 1
+	header[212] = 1
+
+	// size of the data after the header (the actual p15 file)
+	size := make([]byte, 4)
+	binary.LittleEndian.PutUint32(size, uint32(len(p15File)))
+	copy(header[216:], size)
+
+	// check sums (CRC Table)
+	checksumTable := crc16.MakeTable(crc16.CRC16_XMODEM)
+
+	// file checksum
+	fileChecksum := make([]byte, 4)
+	binary.LittleEndian.PutUint16(fileChecksum, crc16.Checksum(p15File, checksumTable))
+	copy(header[220:], fileChecksum)
+
+	// header checksum
+	headerChecksum := make([]byte, 4)
+	binary.LittleEndian.PutUint16(headerChecksum, crc16.Checksum(header[:224], checksumTable))
+	copy(header[224:], headerChecksum)
+
+	// this was in original code but
+
+	return header, nil
+}

go.mod

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+module temp
+
+go 1.21
+
+require github.com/sigurn/crc16 v0.0.0-20211026045750-20ab5afb07e3

go.sum

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+github.com/sigurn/crc16 v0.0.0-20211026045750-20ab5afb07e3 h1:aQKxg3+2p+IFXXg97McgDGT5zcMrQoi0EICZs8Pgchs=
+github.com/sigurn/crc16 v0.0.0-20211026045750-20ab5afb07e3/go.mod h1:9/etS5gpQq9BJsJMWg1wpLbfuSnkm8dPF6FdW2JXVhA=

main.go

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+package main
+
+import (
+	"log"
+	"os"
+)
+
+func main() {
+	p15Bytes, err := os.ReadFile("./apc9138a8cert-no-header.p15")
+	if err != nil {
+		panic(err)
+	}
+
+	apcHeader, err := makeFileHeader(p15Bytes)
+	if err != nil {
+		panic(err)
+	}
+
+	wizardBytes, err := os.ReadFile("./apc9138a.apc-wizard.p15")
+	if err != nil {
+		panic(err)
+	}
+
+	wizHeader := wizardBytes[:228]
+
+	log.Println(apcHeader)
+	log.Println(wizHeader)
+
+	for i := range wizHeader {
+		if apcHeader[i] != wizHeader[i] {
+			panic(i)
+		}
+	}
+
+	log.Println("match")
+
+}