base32: Add base32_decode family of functions

base32.c

@@ -22,10 +22,16 @@
 
 #include "base32.h"
 
+#include <string.h>
+
 const char *BASE32_ALPHABET_RFC4648 = "ABCDEFGHIJKLMNOPQRSTUVWXYZ23456789";
 
 static inline void base32_5to8(const uint8_t *in, uint8_t length, uint8_t *out);
+static inline bool base32_8to5(const uint8_t *in, uint8_t length, uint8_t *out, const char *alphabet);
+static inline void base32_8to5_raw(const uint8_t *in, uint8_t length, uint8_t *out);
+
 static inline int base32_encode_character(uint8_t decoded, const char *alphabet);
+static inline int base32_decode_character(char encoded, const char *alphabet);
 
 bool base32_encode(const uint8_t *in, size_t inlen, char *out, size_t outlen, const char *alphabet) {
 	size_t length = base32_encoded_length(inlen);
@@ -45,6 +51,19 @@ bool base32_encode(const uint8_t *in, size_t inlen, char *out, size_t outlen, co
 	return true;
 }
 
+uint8_t *base32_decode(const char *in, size_t inlen, uint8_t *out, size_t outlen, const char *alphabet) {
+	size_t length = base32_decoded_length(inlen);
+	if (outlen < length) {
+		return NULL;
+	}
+
+	if (!base32_decode_unsafe((uint8_t *) in, inlen, (uint8_t *) out, alphabet)) {
+		return NULL;
+	}
+
+	return &out[length];
+}
+
 void base32_encode_unsafe(const uint8_t *in, size_t inlen, uint8_t *out) {
 	uint8_t remainder = inlen % 5;
 	size_t limit = inlen - remainder;
@@ -57,6 +76,24 @@ void base32_encode_unsafe(const uint8_t *in, size_t inlen, uint8_t *out) {
 	if (remainder) base32_5to8(&in[i], remainder, &out[j]);
 }
 
+bool base32_decode_unsafe(const uint8_t *in, size_t inlen, uint8_t *out, const char *alphabet) {
+	uint8_t remainder = inlen % 8;
+	size_t limit = inlen - remainder;
+
+	size_t i, j;
+	for (i = 0, j = 0; i < limit; i += 8, j += 5) {
+		if (!base32_8to5(&in[i], 8, &out[j], alphabet)) {
+			return false;
+		}
+	}
+
+	if (remainder && !base32_8to5(&in[i], remainder, &out[j], alphabet)) {
+		return false;
+	}
+
+	return true;
+}
+
 size_t base32_encoded_length(size_t inlen) {
 	uint8_t remainder = inlen % 5;
 
@@ -98,6 +135,61 @@ void base32_5to8(const uint8_t *in, uint8_t length, uint8_t *out) {
 	}
 }
 
+bool base32_8to5(const uint8_t *in, uint8_t length, uint8_t *out, const char *alphabet) {
+	if (length == 1 || length == 3 || length == 6 || length > 8) {
+		return false;
+	}
+
+	if (alphabet) {
+		uint8_t decoded[length];
+
+		for (size_t i = 0; i < length; i++) {
+			int ret = base32_decode_character(in[i], alphabet);
+
+			if (ret == -1) {
+				return false;
+			} else {
+				decoded[i] = ret;
+			}
+		}
+
+		base32_8to5_raw(decoded, length, out);
+	} else {
+		base32_8to5_raw(in, length, out);
+	}
+
+	return true;
+}
+
+void base32_8to5_raw(const uint8_t *in, uint8_t length, uint8_t *out) {
+	if (length >= 2) {
+		out[0]  = (in[0] << 3);
+		out[0] |= (in[1] >> 2);
+	}
+
+	if (length >= 4) {
+		out[1]  = (in[1] &  3) << 6;
+		out[1] |= (in[2] << 1);
+		out[1] |= (in[3] >> 4);
+	}
+
+	if (length >= 5) {
+		out[2]  = (in[3] & 15) << 4;
+		out[2] |= (in[4] >> 1);
+	}
+
+	if (length >= 7) {
+		out[3]  = (in[4] &  1) << 7;
+		out[3] |= (in[5] << 2);
+		out[3] |= (in[6] >> 3);
+	}
+
+	if (length >= 8) {
+		out[4]  = (in[6] &  7) << 5;
+		out[4] |= (in[7] & 31);
+	}
+}
+
 int base32_encode_character(uint8_t decoded, const char *alphabet) {
 	if (decoded >> 5) {
 		return -1;
@@ -113,3 +205,25 @@ int base32_encode_character(uint8_t decoded, const char *alphabet) {
 
 	return alphabet[decoded];
 }
+
+int base32_decode_character(char encoded, const char *alphabet) {
+	if (alphabet == BASE32_ALPHABET_RFC4648) {
+		if (encoded >= 'A' && encoded <= 'Z') {
+			return encoded - 'A';
+		} else if (encoded >= 'a' && encoded <= 'z') {
+			return encoded - 'a';
+		} else if (encoded >= '2' && encoded <= '7') {
+			return encoded - '2' + 26;
+		} else {
+			return -1;
+		}
+	}
+
+	const char *occurrence = strchr(alphabet, encoded);
+
+	if (occurrence) {
+		return occurrence - alphabet;
+	} else {
+		return -1;
+	}
+}

base32.h

@@ -32,6 +32,9 @@ extern const char *BASE32_ALPHABET_RFC4648;
 bool base32_encode(const uint8_t *in, size_t inlen, char *out, size_t outlen, const char *alphabet);
 void base32_encode_unsafe(const uint8_t *in, size_t inlen, uint8_t *out);
 
+uint8_t *base32_decode(const char *in, size_t inlen, uint8_t *out, size_t outlen, const char *alphabet);
+bool base32_decode_unsafe(const uint8_t *in, size_t inlen, uint8_t *out, const char *alphabet);
+
 size_t base32_encoded_length(size_t inlen);
 size_t base32_decoded_length(size_t inlen);
 

test_check.c

@@ -527,8 +527,14 @@ START_TEST(test_base32_rfc4648)
 		ck_assert_int_eq(outlen, base32_encoded_length(inlen));
 		ck_assert_int_eq(inlen, base32_decoded_length(outlen));
 
-		base32_encode((uint8_t *) in, inlen, buffer, sizeof(buffer), BASE32_ALPHABET_RFC4648);
+		ck_assert(base32_encode((uint8_t *) in, inlen, buffer, sizeof(buffer), BASE32_ALPHABET_RFC4648));
 		ck_assert_str_eq(buffer, out);
+
+		char *ret = (char *) base32_decode(out, outlen, (uint8_t *) buffer, sizeof(buffer), BASE32_ALPHABET_RFC4648);
+		ck_assert(ret);
+
+		*ret = '\0';
+		ck_assert_str_eq(buffer, in);
 	}
 }
 END_TEST