////
Copyright 2024 Peter Dimov
Distributed under the Boost Software License, Version 1.0.
https://www.boost.org/LICENSE_1_0.txt
////

[#ref_sha1]
# <boost/hash2/sha1.hpp>
:idprefix: ref_sha1_

```
#include <boost/hash2/hmac.hpp>
#include <boost/hash2/digest.hpp>

namespace boost {
namespace hash2 {

class sha1_160;

using hmac_sha1_160 = hmac<sha1_160>;

} // namespace hash2
} // namespace boost
```

This header implements the https://tools.ietf.org/html/rfc3174[SHA-1 algorithm].

## sha1_160

```
class sha1_160
{
public:

    using result_type = digest<20>;

    static constexpr std::size_t block_size = 64;

    constexpr sha1_160();
    explicit constexpr sha1_160( std::uint64_t seed );
    sha1_160( void const* p, std::size_t n );
    constexpr sha1_160( unsigned char const* p, std::size_t n );

    void update( void const* p, std::size_t n );
    constexpr void update( unsigned char const* p, std::size_t n );

    constexpr result_type result();
};
```

### Constructors

```
constexpr sha1_160();
```

Default constructor.

Effects: ::
  Initializes the internal state of the SHA-1 algorithm to its initial values.

```
explicit constexpr sha1_160( std::uint64_t seed );
```

Constructor taking an integer seed value.

Effects: ::
  Initializes the state as if by default construction, then if `seed` is not zero, performs `update(p, 8); result();` where `p` points to a little-endian representation of the value of `seed`.

Remarks: ::
  By convention, if `seed` is zero, the effect of this constructor is the same as default construction.

```
sha1_160( void const* p, std::size_t n );
constexpr sha1_160( unsigned char const* p, std::size_t n );
```

Constructor taking a byte sequence seed.

Effects: ::
  Initializes the state as if by default construction, then if `n` is not zero, performs `update(p, n); result()`.

Remarks: ::
  By convention, if `n` is zero, the effect of this constructor is the same as default construction.

### update

```
void update( void const* p, std::size_t n );
constexpr void update( unsigned char const* p, std::size_t n );
```

Effects: ::
  Updates the internal state of the SHA-1 algorithm from the byte sequence `[p, p+n)`.

Remarks: ::
  Consecutive calls to `update` are equivalent to a single call with the concatenated byte sequences of the individual calls.

### result

```
constexpr result_type result();
```

Effects: ::
  Pads the accumulated message and finalizes the SHA-1 digest.

Returns: ::
  The SHA-1 digest of the message formed from the byte sequences of the preceding calls to `update`.

Remarks: ::
  Repeated calls to `result()` return a pseudorandom sequence of `result_type` values, effectively extending the output.

