# Hash generator and checksum calculator (MD5, SHA-256)

> Generate MD5, SHA-1, SHA-256, SHA-512 and CRC-32 hashes of any text, check them against a published checksum, and see the avalanche effect.

Versión interactiva: https://www.calcopenly.com/es/programming/hash-checksum-calculator
Tema: Calculadoras de programación y tecnología

A cryptographic hash turns any input into a fixed-size digest: 128 bits for MD5, 160 for SHA-1, 256 for SHA-256 and 512 for SHA-512, while CRC-32 is a 32-bit error-detecting checksum. The text is encoded as UTF-8, padded to whole 512-bit or 1024-bit blocks, and run through the algorithm's compression rounds as NIST FIPS 180-4 and RFC 1321 specify.

People use it to verify downloads against a published checksum, compare files and test their own code. The default sentence, "The quick brown fox jumps over the lazy dog", has the SHA-256 digest d7a8fbb3…37c9e592, and flipping one input bit changes 141 of its 256 bits, close to the half a good hash should change.

MD5 and SHA-1 have practical collision attacks, so use SHA-256 or SHA-512 wherever someone could tamper with the data.

## Datos

- **Texto**: Hashed as UTF-8 bytes. Line breaks count as a single line feed (\n).
- **Algorithm** (opciones: MD5, SHA-1, SHA-256, SHA-512, CRC-32)
- **Show digests as** (opciones: hex, HEX, Base64)
- **Add a line feed at the end**: Matches `echo text | sha256sum`, which hashes the text followed by a line feed.
- **Compare with checksum**

## Resultados

- Digest — resultado principal
- Comparison
- MD5
- SHA-1
- SHA-256
- SHA-512
- CRC-32
- Input size (bytes)
- Digest size (bits)
- Digest bits changed by flipping one input bit (bits)

## Fórmula

$$
\begin{aligned} \text{blocks} &= \left\lfloor \frac{n + 8}{64} \right\rfloor + 1 && \text{MD5, SHA-1, SHA-256} \\ \text{blocks} &= \left\lfloor \frac{n + 16}{128} \right\rfloor + 1 && \text{SHA-512} \end{aligned}
$$

## Ejemplos resueltos

### “abc” (FIPS 180-4 one-block example)

- Texto: abc
- Algorithm: SHA-256
- Show digests as: hex
- **Digest: ba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad**
- **MD5: 900150983cd24fb0d6963f7d28e17f72**
- **SHA-1: a9993e364706816aba3e25717850c26c9cd0d89d**
- **SHA-512: ddaf35a193617abacc417349ae20413112e6fa4e89a97ea20a9eeee64b55d39a2192992a274fc1a836ba3c23a3feebbd454d4423643ce80e2a9ac94fa54ca49f**
- **CRC-32: 352441c2**
- **Input size: 3 bytes**
- Fuente de comprobación: FIPS 180-4 / NIST CSRC SHA-1, SHA-256, SHA-512 examples for “abc”; RFC 1321 §A.5 MD5 test suite; all five re-checked with Python 3.8 hashlib and binascii.crc32

### Empty string

- Algorithm: SHA-512
- Show digests as: hex
- **Digest: cf83e1357eefb8bdf1542850d66d8007d620e4050b5715dc83f4a921d36ce9ce47d0d13c5d85f2b0ff8318d2877eec2f63b931bd47417a81a538327af927da3e**
- **MD5: d41d8cd98f00b204e9800998ecf8427e**
- **SHA-1: da39a3ee5e6b4b0d3255bfef95601890afd80709**
- **SHA-256: e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855**
- **CRC-32: 00000000**
- **Input size: 0 bytes**
- Fuente de comprobación: RFC 1321 §A.5 (MD5 of ""); Python 3.8 hashlib.md5/sha1/sha256/sha512(b'').hexdigest() and binascii.crc32(b'')

### 448-bit message (two blocks for SHA-256)

- Texto: abcdbcdecdefdefgefghfghighijhijkijkljklmklmnlmnomnopnopq
- Algorithm: SHA-256
- Show digests as: hex
- **Digest: 248d6a61d20638b8e5c026930c3e6039a33ce45964ff2167f6ecedd419db06c1**
- **SHA-1: 84983e441c3bd26ebaae4aa1f95129e5e54670f1**
- **SHA-512: 204a8fc6dda82f0a0ced7beb8e08a41657c16ef468b228a8279be331a703c33596fd15c13b1b07f9aa1d3bea57789ca031ad85c7a71dd70354ec631238ca3445**
- **Input size: 56 bytes**
- Fuente de comprobación: FIPS 180-4 / NIST CSRC two-block examples for the 448-bit message; re-checked with Python 3.8 hashlib

### 896-bit message (two blocks for SHA-512)

- Texto: abcdefghbcdefghicdefghijdefghijkefghijklfghijklmghijklmnhijklmnoijklmnopjklmn…
- Algorithm: SHA-512
- Show digests as: hex
- **Digest: 8e959b75dae313da8cf4f72814fc143f8f7779c6eb9f7fa17299aeadb6889018501d289e4900f7e4331b99dec4b5433ac7d329eeb6dd26545e96e55b874be909**
- Fuente de comprobación: FIPS 180-4 / NIST CSRC SHA-512 two-block example; re-checked with Python 3.8 hashlib.sha512

### MD5 test suite: “message digest”

- Texto: message digest
- Algorithm: MD5
- Show digests as: hex
- **Digest: f96b697d7cb7938d525a2f31aaf161d0**
- Fuente de comprobación: RFC 1321 §A.5 test suite; re-checked with Python 3.8 hashlib.md5

### MD5 test suite: 80 digits (two blocks)

- Texto: 12345678901234567890123456789012345678901234567890123456789012345678901234567890
- Algorithm: MD5
- Show digests as: hex
- **Digest: 57edf4a22be3c955ac49da2e2107b67a**
- **Input size: 80 bytes**
- Fuente de comprobación: RFC 1321 §A.5 test suite; re-checked with Python 3.8 hashlib.md5

## Preguntas

### Is MD5 still safe to use?

Not for security. Practical MD5 collisions were published in 2004, and in 2008 researchers used them to forge a trusted certificate authority certificate. RFC 6151 (2011) says MD5 is no longer acceptable where collision resistance is required, such as digital signatures. It still catches accidental corruption in a download, but use SHA-256 or SHA-512 from NIST FIPS 180-4 for anything an attacker could alter.

### What is the difference between SHA-1 and SHA-256?

SHA-256 produces a 256-bit digest (64 hex digits) against SHA-1's 160 bits (40 hex digits), and unlike SHA-1 it has no known practical collision attack. Google and CWI Amsterdam published the first SHA-1 collision, SHAttered, in 2017, and NIST has announced that SHA-1 is to be phased out of all its uses by 31 December 2030. Both belong to FIPS 180-4.

### How do I verify a file's checksum?

Hash the downloaded file and compare the result with the checksum the publisher lists; any difference means the file changed. On Linux run sha256sum file, on macOS shasum -a 256 file, and on Windows certutil -hashfile file SHA256 or PowerShell's Get-FileHash, which uses SHA-256 by default. The comparison box here does the same for text and ignores case and spaces.

### Why does echo text | sha256sum give a different hash?

Because echo adds a line feed, so the command hashes abc plus a newline (4 bytes) rather than abc (3 bytes), and one extra byte changes the whole digest: SHA-256 of abc starts ba7816bf, while abc with a line feed starts edeaaff3. Use echo -n or printf '%s' to hash the text alone, or turn on the line-feed option here to match echo.

### Can two different inputs have the same hash?

Yes, because unlimited inputs map to a fixed number of digests, but for a secure hash nobody should be able to find such a pair. By the birthday bound, a brute-force search needs about 2^(n/2) tries for an n-bit digest: 2^64 for MD5 and 2^128 for SHA-256. Known attacks find MD5 and SHA-1 collisions far faster, and CRC-32 collisions can be computed directly because CRC is linear.

### ¿Qué precisión tiene «Hash generator and checksum calculator (MD5, SHA-256)»?

La precisión depende de tus datos y de los supuestos del método. El cálculo decimal usa 50 cifras significativas, pero las estimaciones, los métodos numéricos y los datos de origen pueden ser menos precisos; el redondeo mostrado no elimina esos límites. Ejemplos resueltos comprobados con fuentes independientes: 11. Por ejemplo, «“abc” (FIPS 180-4 one-block example)» se comprueba con FIPS 180-4 / NIST CSRC SHA-1, SHA-256, SHA-512 examples for “abc”; RFC 1321 §A.5 MD5 test suite; all five re-checked with Python 3.8 hashlib and binascii.crc32.

### ¿De dónde procede el método?

NIST FIPS 180-4, Secure Hash Standard (SHA-1, SHA-256, SHA-512); RFC 1321 — The MD5 Message-Digest Algorithm; NIST CSRC — Examples with intermediate values (SHA-1, SHA-2); Catalogue of parametrised CRC algorithms — CRC-32/ISO-HDLC.

## Fuentes

- [NIST FIPS 180-4, Secure Hash Standard (SHA-1, SHA-256, SHA-512)](https://csrc.nist.gov/pubs/fips/180-4/upd1/final)
- [RFC 1321 — The MD5 Message-Digest Algorithm](https://www.rfc-editor.org/rfc/rfc1321)
- [NIST CSRC — Examples with intermediate values (SHA-1, SHA-2)](https://csrc.nist.gov/projects/cryptographic-standards-and-guidelines/example-values)
- [Catalogue of parametrised CRC algorithms — CRC-32/ISO-HDLC](https://reveng.sourceforge.io/crc-catalogue/all.htm#crc.cat.crc-32-iso-hdlc)