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Diffstat (limited to 'src/libzrtpcpp/Base32.h')

-rw-r--r-- | src/libzrtpcpp/Base32.h | 228 |

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diff --git a/src/libzrtpcpp/Base32.h b/src/libzrtpcpp/Base32.h new file mode 100644 index 0000000..fbe2983 --- /dev/null +++ b/src/libzrtpcpp/Base32.h @@ -0,0 +1,228 @@ +#ifndef BASE32_H +#define BASE32_H + +/* + * + * Copyright (c) 2002 Bryce "Zooko" Wilcox-O'Hearn Permission is hereby + * granted, free of charge, to any person obtaining a copy of this software to + * deal in this software without restriction, including without limitation the + * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or + * sell copies of this software, and to permit persons to whom this software + * is furnished to do so, subject to the following conditions: + * + * The above copyright notice and this permission notice shall be included in + * all copies or substantial portions of this software. + * + * THIS SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR + * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, + * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE + * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER + * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING + * FROM, OUT OF OR IN CONNECTION WITH THIS SOFTWARE OR THE USE OR OTHER + * DEALINGS IN THIS SOFTWARE. + * + * Converted to C++ by: + * @author Werner Dittmann <Werner.Dittmann@t-online.de> + */ + +/** + * @file Base32.h + * @brief C++ implmentation of the Base32 encoding and decoding + * + * ZRTP uses the base 32 encoding and decoding to generate the Short + * Authentication String (SAS). + * + * @ingroup GNU_ZRTP + * @{ + */ + +#include <iostream> +#include <cstdlib> + +#include <string.h> +#include <assert.h> +#include <stddef.h> + +using namespace std; + +extern int divceil(int a, int b); + +class Base32 { + + public: + + /** + * A Constructor that decodes from base32 into binary. + * + * The constructor decodes the base32 encoded data back into binary + * data. Use <code>getDecoded(...)</code> to get the binary data. + * + * @param encoded + * The string that contains the base32 encoded data. + */ + Base32(const string encoded); + + /** + * A Constructor that decodes from base32 into binary. + * + * This constructor decodes the base32 encoded data back into + * binary data. Only the specified number of bits are decoded + * (should be a multiple of 5). Use + * <code>getDecoded(...)</code> to get the binary data. + * + * @param encoded + * The string that contains the base32 encoded data. + * @param noOfBits + * How many bits to decode into binary data. + */ + Base32(const string encoded, int noOfBits); + + /** + * A Constructor that encodes binary data. + * + * The constructor converts the first specified number of bits of + * the binary data into a base32 presentation. Use + * <code>getEncoded</code> to get the encoded data. + * + * @param data + * A pointer to the first bits (byte) of binary data + * @param noOfBits + * How many bits to use for encoding. Should be a + * multiple of 5. + */ + Base32(const unsigned char* data, int noOfBits); + + ~Base32(); + + /** + * Get the decoded binary data and its length. + * + * The method returns the decoded binary data if the appropriate + * Constructor was used. Otherwise we return <code>NULL</code> + * pointer and length zero. + * + * <em>Note:</em> This method returns a pointer to the decoded + * binary data. The Base32 object manages this pointer, thus you + * may need to copy the data to a save place before deleting this + * object. If the object is deleted this pointer is no longer + * valid. + * + * @param length + * A reference to an integer. + * @return + * A pointer to the decoded binary data. + */ + const unsigned char* getDecoded(int &length); + + /** + * Get the encoded base32 string. + * + * The method returns a string that contains the base32 encoded + * data if the appropriate constructor was used. Otherwise we + * return an empty string. + * + * @return + * The string containing the base32 encoded data. + */ + const string getEncoded() { return encoded; }; + + /** + * Compute the number of base32 encoded characters given the + * number of bits. + * + * @param lengthInBits + * The length of the data in bits + * @return + * The length of the base-32 encoding of the data in characters + */ + static size_t const b2alen(const size_t lengthInBits) { + return divceil(lengthInBits, 5); }; + + private: + + /** + * Decodes a string with base32 presentation into binary data. + * + * a2b_l() will return a result big enough to hold lengthinbits bits. So + * for example if cs is 4 characters long (encoding at least 15 and up to + * 20 bits) and lengthinbits is 16, then a2b_l() will return a string of + * length 2 (since 2 bytes is sufficient to store 16 bits). If cs is 4 + * characters long and lengthinbits is 20, then a2b_l() will return a + * string of length 3 (since 3 bytes is sufficient to store 20 bits). Note + * that `b2a_l()' does not mask off unused least-significant bits, so for + * example if cs is 4 characters long and lengthinbits is 17, then you + * must ensure that all three of the unused least-significant bits of cs + * are zero bits or you will get the wrong result. This precondition is + * tested by assertions if assertions are enabled. (Generally you just + * require the encoder to ensure this consistency property between the + * least significant zero bits and value of `lengthinbits', and reject + * strings that have a length-in-bits which isn't a multiple of 8 and yet + * don't have trailing zero bits, as improperly encoded.) + * + * @param cs + * The data to be decoded + * @param size + * The length of the input data buffer. Usually divceil(length in bits, 5). + * @param lengthinbits + * The number of bits of data in <code>cs</code> to be decoded + */ + void a2b_l(const string cs, size_t size, const size_t lengthinbits); + + /** + * Encodes binary to to base32 presentation. + * + * b2a_l() will generate a base-32 encoded string big enough to encode + * lengthinbits bits. So for example if os is 2 bytes long and + * lengthinbits is 15, then b2a_l() will generate a 3-character- long + * base-32 encoded string (since 3 quintets is sufficient to encode 15 + * bits). If os is 2 bytes long and lengthinbits is 16 (or None), then + * b2a_l() will generate a 4-character string. Note that `b2a_l()' does + * not mask off unused least-significant bits, so for example if os is 2 + * bytes long and lengthinbits is 15, then you must ensure that the unused + * least-significant bit of os is a zero bit or you will get the wrong + * result. This precondition is tested by assertions if assertions are + * enabled. + * + * Warning: if you generate a base-32 encoded string with `b2a_l()', and + * then someone else tries to decode it by calling `a2b()' instead of + * `a2b_l()', then they will (probably) get a different string than the + * one you encoded! So only use `b2a_l()' when you are sure that the + * encoding and decoding sides know exactly which `lengthinbits' to use. + * If you do not have a way for the encoder and the decoder to agree upon + * the lengthinbits, then it is best to use `b2a()' and `a2b()'. The only + * drawback to using `b2a()' over `b2a_l()' is that when you have a number + * of bits to encode that is not a multiple of 8, `b2a()' can sometimes + * generate a base-32 encoded string that is one or two characters longer + * than necessary. + * + * @param cs + * Pointer to binary data. + * @param len + * Length of the binary data buffer. Usually (noOfBits+7)/8. + * @param noOfBits + * The number of bits of data in encoded into `cs' + */ + void b2a_l(const unsigned char* cs, int len, const size_t noOfBits); + + /** + * Holds the pointer to decoded binary data + */ + unsigned char *binaryResult; + + /** + * Length of decoding result + */ + int resultLength; + + /** + * The string containing the base32 encoded data. + */ + string encoded; + + unsigned char smallBuffer[128]; +}; + +/** + * @} + */ +#endif |