# Hash and digest functions

Checksum and digest functions summarize text or binary input. CRC functions return integer checksums, named SHA/MD5 functions return hexadecimal text, and `digest`/`hmac` expose binary results for a chosen algorithm.

SQL NULL and binary zero bytes follow the individual contracts below. Use `encode` to display a binary digest in hex.

## Example: Comparing checksums and digests

```sql
SELECT crc32('123456789'), md5('hello') = md5('hello')
FORMAT csv;
```

```text
3421780262,1
```

## crc32

Compute the IEEE CRC-32 checksum.

### Syntax

```text
crc32(bytes)
```

### Arguments

Native BLOB or UTF-8 text; includes embedded zero bytes. SQL NULL propagates.

### Returned value

Nonnegative INTEGER unsigned 32-bit checksum; empty input gives zero.

### Example

```sql
SELECT crc32('123456789') FORMAT csv;
```

```text
3421780262
```

## crc32c

Compute the Castagnoli CRC-32C checksum.

### Syntax

```text
crc32c(bytes)
```

### Arguments

Native BLOB or UTF-8 text; includes embedded zero bytes. SQL NULL propagates.

### Returned value

Nonnegative INTEGER unsigned 32-bit checksum; empty input gives zero.

### Example

```sql
SELECT crc32c('123456789') FORMAT csv;
```

```text
3808858755
```

## digest

Compute an algorithm-selected binary hash.

### Syntax

```text
digest(data,algorithm)
```

### Arguments

BLOB or UTF-8 text; md5/sha1/sha224/sha256/sha384/sha512, case-insensitive algorithm names. SQL NULL propagates.

### Returned value

BLOB digest.

### Example

```sql
SELECT encode(digest('abc','sha256'),'hex') FORMAT csv;
```

```text
"ba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad"
```

## hmac

Compute an RFC 2104 keyed message authentication code.

### Syntax

```text
hmac(data,key,algorithm)
```

### Arguments

Same byte/algorithm rules as digest. SQL NULL propagates.

### Returned value

BLOB authentication code.

### Example

```sql
SELECT encode(hmac('data','key','sha256'),'hex') FORMAT csv;
```

```text
"5031fe3d989c6d1537a013fa6e739da23463fdaec3b70137d828e36ace221bd0"
```

## md5

Compute the lowercase hexadecimal MD5 digest of text bytes.

### Syntax

```text
md5(text)
```

### Arguments

Text conversion uses UTF-8 bytes; NULL propagates.

### Returned value

32-character lowercase hexadecimal TEXT.

### Example

```sql
SELECT md5('abc') FORMAT csv;
```

```text
"900150983cd24fb0d6963f7d28e17f72"
```

## sha224

Compute the SHA-224 digest of exact input bytes.

### Syntax

```text
sha224(bytes)
```

### Arguments

Text supplies UTF-8 bytes; BLOB supplies exact bytes. NULL propagates.

### Returned value

BLOB of 28 digest bytes.

### Example

```sql
SELECT length(sha224('abc')) FORMAT csv;
```

```text
28
```

## sha256

Compute SHA-256 over exact input bytes.

### Syntax

```text
sha256(bytes)
```

### Arguments

Text supplies UTF-8 bytes; BLOB retains every byte.

### Returned value

32-byte BLOB; use encode(...,hex) for hexadecimal text; SQL NULL propagates.

### Example

```sql
SELECT encode(sha256('abc'),'hex') FORMAT csv;
```

```text
"ba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad"
```

## sha384

Compute the SHA-384 digest of exact input bytes.

### Syntax

```text
sha384(bytes)
```

### Arguments

Text supplies UTF-8 bytes; BLOB supplies exact bytes. NULL propagates.

### Returned value

BLOB of 48 digest bytes.

### Example

```sql
SELECT length(sha384('abc')) FORMAT csv;
```

```text
48
```

## sha512

Compute SHA-512 over exact input bytes.

### Syntax

```text
sha512(bytes)
```

### Arguments

Text supplies UTF-8 bytes; BLOB retains every byte.

### Returned value

64-byte BLOB; SQL NULL propagates.

### Example

```sql
SELECT length(sha512('abc')) FORMAT csv;
```

```text
64
```