diff options
Diffstat (limited to 'lib.go')
| -rw-r--r-- | lib.go | 28 |
1 files changed, 28 insertions, 0 deletions
@@ -15,6 +15,8 @@ import ( "io" "log" "math" + "strconv" + "strings" "unicode" ) @@ -199,3 +201,29 @@ func namespaceStrictToTransitional(content []byte) []byte { } return content } + +// genSheetPasswd provides a method to generate password for worksheet +// protection by given plaintext. When an Excel sheet is being protected with +// a password, a 16-bit (two byte) long hash is generated. To verify a +// password, it is compared to the hash. Obviously, if the input data volume +// is great, numerous passwords will match the same hash. Here is the +// algorithm to create the hash value: +// +// take the ASCII values of all characters shift left the first character 1 bit, the second 2 bits and so on (use only the lower 15 bits and rotate all higher bits, the highest bit of the 16-bit value is always 0 [signed short]) +// XOR all these values +// XOR the count of characters +// XOR the constant 0xCE4B +func genSheetPasswd(plaintext string) string { + var password int64 = 0x0000 + var charPos uint = 1 + for _, v := range plaintext { + value := int64(v) << charPos + charPos++ + rotatedBits := value >> 15 // rotated bits beyond bit 15 + value &= 0x7fff // first 15 bits + password ^= (value | rotatedBits) + } + password ^= int64(len(plaintext)) + password ^= 0xCE4B + return strings.ToUpper(strconv.FormatInt(password, 16)) +} |