Hex and Base64 encode and decode. These are codecs, not cryptographic primitives.

Allocating helpers return a heap buffer the caller must free. *_into writes into a caller-owned buffer and returns 0 on success or -1 on error (NULL arguments, size wrap, or dest_cap too small). Decode is fail-closed: invalid input returns an error and does not publish an output size.

Hex strings are lowercase with no leading 0x. hex_decode / hex_decode_into accept optional 0x or 0X.

Functions

b64_encode / b64_encode_into

char *b64_encode(const unsigned char *s, size_t sz);
int b64_encode_into(const unsigned char *s, size_t sz, char *dest, size_t dest_cap);

/* Usage */
char *encoded = b64_encode((unsigned char *)"Hello", 5);
/* encoded: "SGVsbG8=" */
free(encoded);

char buf[16];
b64_encode_into((unsigned char *)"Hello", 5, buf, sizeof buf);

dest_cap must be at least 4 * ceil(sz / 3) + 1 (NUL included).

b64_decode / b64_decode_into

Invalid characters, truncated input, and incomplete padding return an error. A valid prefix of a corrupt string is not returned. The allocating form is NUL-terminated but may contain interior NULs, so use decode_sz, not strlen. *decode_sz is written only on success.

unsigned char *b64_decode(const char *s, size_t sz, size_t *decode_sz);
int b64_decode_into(const char *s, size_t sz, unsigned char *dest, size_t dest_cap,
                    size_t *decode_sz);

/* Usage */
size_t out_sz;
unsigned char *decoded = b64_decode("SGVsbG8=", 8, &out_sz);
/* decoded: "Hello", out_sz: 5 */
free(decoded);

hex_encode / hex_encode_into

[0xDE, 0xAD, 0xBE, 0xEF] becomes "deadbeef". Returns NULL / -1 if sz * 2 + 1 would wrap size_t or dest_cap is smaller than that.

char *hex_encode(const unsigned char *hex, size_t sz);
int hex_encode_into(const unsigned char *src, size_t n, char *dest, size_t dest_cap);

hex_decode / hex_decode_into

Odd-length input is padded with a leading nibble of 0. Returns NULL / -1 if any character is not a hex digit. *sz / *out_sz is written only on success.

unsigned char *hex_decode(const char *orig, size_t *sz);
int hex_decode_into(const char *src, unsigned char *dest, size_t dest_cap, size_t *out_sz);

hex_to_str

Copies bytes into a freshly allocated C string. Not hex encoding.

char *hex_to_str(const unsigned char *hex, size_t sz);