mirror of
https://github.com/gregtwallace/apc-p15-tool.git
synced 2025-01-22 08:14:08 +00:00
75 lines
2.6 KiB
Go
75 lines
2.6 KiB
Go
package app
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import (
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"encoding/binary"
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"errors"
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"github.com/sigurn/crc16"
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)
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// makeFileHeader generates the 228 byte header to prepend to the .p15
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// as required by APC UPS NMC. Only 2,048 bit RSA keys are supported
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// so the header will always be written with that key size assumption
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func makeFileHeader(p15File []byte) ([]byte, error) {
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// original reference code from: https://github.com/bbczeuz/apc_tools
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// // add APC header
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// *(uint32_t *)(buf + 0) = 1; // always 1
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// *(uint32_t *)(buf + 4) = 1; // always 1
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// strncpy((char *)(buf + 8), "SecurityWizard103", 0xC8); // apparently supposed to identify the creating tool, SecWiz v1.04 sill puts 103 here
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// *(uint32_t *)(buf + 208) = 1; // always 1
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// *(uint32_t *)(buf + 212) = 1; // always 1
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// *(uint32_t *)(buf + 216) = fileSize; // size of the following data
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// *(uint32_t *)(buf + 208) = keySize; // 1 for 1024 key, otherwise (2048 bit) 2
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// // 16 bit checksums are moved to 32 bit int with sign-extension
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// *(uint32_t *)(buf + 220) = (int32_t)calc_cksum(0, buf + 228, fileSize); // checksum of the original file
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// *(uint32_t *)(buf + 224) = (int32_t)calc_cksum(0, buf, 224); // checksum of the APC header
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// NOTE: This line is unused as it seems the APC CLI tool v1.0.0 code always writes this as a 1 (regardless of key length)
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// *(uint32_t *)(buf + 208) = keySize; // 1 for 1024 key, otherwise (2048 bit) 2
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// Unsure why this was in original code but seems irrelevant
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header := make([]byte, 228)
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// always 1
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header[0] = 1
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// always 1
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header[4] = 1
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// apparently supposed to identify the creating tool
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toolName := "NMCSecurityWizardCLI100"
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toolNameBytes := []byte(toolName)
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if len(toolNameBytes) > 200 {
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return nil, errors.New("tool name is too big to fit in header")
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}
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copy(header[8:], toolNameBytes)
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// always 1
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header[208] = 1
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// always 1
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header[212] = 1
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// size of the data after the header (the actual p15 file)
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size := make([]byte, 4)
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binary.LittleEndian.PutUint32(size, uint32(len(p15File)))
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copy(header[216:], size)
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// check sums (CRC Table)
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checksumTable := crc16.MakeTable(crc16.CRC16_XMODEM)
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// NOTE: 16 bit checksums are moved to 32 bit int with sign-extension by converting
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// to int16 and then to uint32
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// file checksum
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fileChecksum := make([]byte, 4)
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binary.LittleEndian.PutUint32(fileChecksum, uint32(int16(crc16.Checksum(p15File, checksumTable))))
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copy(header[220:], fileChecksum)
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// header checksum
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headerChecksum := make([]byte, 4)
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binary.LittleEndian.PutUint32(headerChecksum, uint32(int16(crc16.Checksum(header[:224], checksumTable))))
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copy(header[224:], headerChecksum)
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return header, nil
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}
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