4 ms·

Like this: use sha2::{Sha256, Digest}; fn main() { let mut hasher = Sha256::new(); hasher.input(b"hello world"); let result = hasher.result();

Like this: use sha2::{Sha256, Digest}; fn main() { let mut hasher = Sha256::new(); hasher.input(b"hello world"); let result = hasher.result(); ?? } How do I get a string with the hash value? Which chapter of which book should I read?

aisengard 7y ago
The hash value is a bunch of bytes. A "string" would need to be some encoded version of those bytes, commonly hexadecimal representation.
chousuke 7y ago
I think you can use format!() to format the byte array as a hex string. The result of a hash is never a string, so it makes sense that you'd need another step to print it as one.
steveklabnik 7y ago
Ah, I see! So yeah, this isn't something the book covers, so that would not be helpful. In this case, the hash ends up being raw bytes. So the question is, what are you trying to do with this hash? Being a bunch of bytes, this may not be valid UTF-8 (and in this case, is not ASCII, let alone UTF-8). One option is to encode to base64: use sha2::{Sha256, Digest}; use base64; fn main() { let mut hasher = Sha256::new(); hasher.input(b"hello world"); let result = hasher.result(); let encoded = base64::encode(&result); assert_eq!("uU0nuZNNPgilLlLX2n2r+sSE7+N6U4DukIj3rOLvzek=", encoded); } But yeah, you can't exactly "get a string" out of a random bag of bytes unless you know how you want that bag of bytes to be represented, encoding wise. That's not exactly a satisfying answer, but such are strings!
Keats 7y ago
As mentioned by others, you need to convert the bytes to a String. `Sha2` provides a helper function for that: `hasher.result_str()`. EDIT: sorry I don't know which docs I was looking at, I can't find it in the current version.
- StreamBright 7y ago
  This is helpful but in general what is a problem of having strings and trivial functions to convert something (like bytes) to strings? Maybe I am missing the point.
  - DougBTX 7y ago
    Rust doesn't have varargs, so formatting functions tend to be macros (allowing to pass in multiple arguments, compile time parsing the format string to allow type checking etc) so they are generally not that trivial. There are some examples of printing output using formatting strings in the RustCrypto readme: let hash = Blake2b::digest(b"my message"); println!("Result: {:x}", hash); https://github.com/RustCrypto/hashes#usage https://github.com/RustCrypto/hashes#usage If you're looking to get the actual string value rather than just print it out, then take a look at the format macro. It uses the same format strings / traits etc as println, so wherever you see println you could drop in format instead: let hash = Blake2b::digest(b"my message"); let text = format!("{:x}", hash); https://doc.rust-lang.org/std/macro.format.html https://doc.rust-lang.org/std/macro.format.html
  - unlinked_dll 7y ago
    Because converting a type to a string isn't trivial. It needs to be defined for that type. Rust does have a pair of traits that can be used, Display [1] and Debug [2]. Display must be implemented manually by the author of a type, while Debug can be automatically derived if all the members of a type implement Debug. Like this: #[derive(Debug)] struct Foo { } [1] https://doc.rust-lang.org/std/fmt/trait.Display.html https://doc.rust-lang.org/std/fmt/trait.Display.html [2] https://doc.rust-lang.org/std/fmt/trait.Debug.html https://doc.rust-lang.org/std/fmt/trait.Debug.html
  - steveklabnik 7y ago
    The process of "functions to convert bytes to a string" is called "encoding". The problem is, there's no universal way to do it, so you need to choose one. You need to know what the bytes mean, and then convert them into whatever representation that you need. It is unfortunate that you’ve been downvoted for asking a question.
McWobbleston 7y ago
I'm well versed in Rust but I think you might need to use str::from_utf8(result.as_slice()) https://docs.rs/generic-array/0.8.2/generic_array/struct.GenericArray.html#method.as_slice https://docs.rs/generic-array/0.8.2/generic_array/struct.Gen... https://doc.rust-lang.org/std/str/fn.from_utf8.html https://doc.rust-lang.org/std/str/fn.from_utf8.html
- kam 7y ago
  That would be correct if the bytes were a string encoded in utf-8, but that's probably not the case for the output of a hash function.
unionpivo 7y ago
since we know that Sha256::new() will always produce 'valid' characters for utf8 you can just do let my_rust_string = str::from_utf8(result).unwarp() If there is a possibility of an error, (you read it from file, network ...) you can do: let my_rust_string = match str::from_utf8(result) { Ok(str) => str, Err(err) => panic!("Invalid utf8: {}", err), }; Or you can do lossy conversion (will have that question mark on chars that it cant decode) let my_rust_string = String::from_utf8_lossy(result); edit: Ok so i read sha2 api wrong. result() is raw bytes and result_str() is hex encoded string. Above wont be much use for either. And others have already explained what to use. I just stared programming in rust several months ago, and that was my pain also, since where i live we still have some other encoding in use.
the8472 7y ago
This seems to be a conceptual mistake that often happens when coming from high level languages, I have seen similar confusion on stack overflow relating to packet based network protocols. What many low-level data formats deal with are raw bytes ("byte strings" in some contexts). The output of a hasher is random binary data. What most humans are accustomed to are some form of encoding that makes it easier to spell out the octets. Hex and base64 are common. But they are not the native representation that the machine deals with. With almost everything being explicit in rust you need an explicit conversion from bytes to hex, base64, urlencode or some other format. Those conversion methods (with their contract often expressed as a separate trait) may be provided by the same crate or you may have to pull them in from a different crate. A hasher does not need to provide this itself because its output types can be enhanced by foreign traits.

aisengard 7y ago

The hash value is a bunch of bytes. A "string" would need to be some encoded version of those bytes, commonly hexadecimal representation.

chousuke 7y ago

I think you can use format!() to format the byte array as a hex string. The result of a hash is never a string, so it makes sense that you'd need another step to print it as one.

steveklabnik 7y ago

Ah, I see! So yeah, this isn't something the book covers, so that would not be helpful. In this case, the hash ends up being raw bytes. So the question is, what are you trying to do with this hash? Being a bunch of bytes, this may not be valid UTF-8 (and in this case, is not ASCII, let alone UTF-8). One option is to encode to base64: use sha2::{Sha256, Digest}; use base64; fn main() { let mut hasher = Sha256::new(); hasher.input(b"hello world"); let result = hasher.result(); let encoded = base64::encode(&result); assert_eq!("uU0nuZNNPgilLlLX2n2r+sSE7+N6U4DukIj3rOLvzek=", encoded); } But yeah, you can't exactly "get a string" out of a random bag of bytes unless you know how you want that bag of bytes to be represented, encoding wise. That's not exactly a satisfying answer, but such are strings!

Keats 7y ago

As mentioned by others, you need to convert the bytes to a String. `Sha2` provides a helper function for that: `hasher.result_str()`. EDIT: sorry I don't know which docs I was looking at, I can't find it in the current version.

StreamBright 7y ago
This is helpful but in general what is a problem of having strings and trivial functions to convert something (like bytes) to strings? Maybe I am missing the point.
- DougBTX 7y ago
  Rust doesn't have varargs, so formatting functions tend to be macros (allowing to pass in multiple arguments, compile time parsing the format string to allow type checking etc) so they are generally not that trivial. There are some examples of printing output using formatting strings in the RustCrypto readme: let hash = Blake2b::digest(b"my message"); println!("Result: {:x}", hash); https://github.com/RustCrypto/hashes#usage https://github.com/RustCrypto/hashes#usage If you're looking to get the actual string value rather than just print it out, then take a look at the format macro. It uses the same format strings / traits etc as println, so wherever you see println you could drop in format instead: let hash = Blake2b::digest(b"my message"); let text = format!("{:x}", hash); https://doc.rust-lang.org/std/macro.format.html https://doc.rust-lang.org/std/macro.format.html
- unlinked_dll 7y ago
  Because converting a type to a string isn't trivial. It needs to be defined for that type. Rust does have a pair of traits that can be used, Display [1] and Debug [2]. Display must be implemented manually by the author of a type, while Debug can be automatically derived if all the members of a type implement Debug. Like this: #[derive(Debug)] struct Foo { } [1] https://doc.rust-lang.org/std/fmt/trait.Display.html https://doc.rust-lang.org/std/fmt/trait.Display.html [2] https://doc.rust-lang.org/std/fmt/trait.Debug.html https://doc.rust-lang.org/std/fmt/trait.Debug.html
- steveklabnik 7y ago
  The process of "functions to convert bytes to a string" is called "encoding". The problem is, there's no universal way to do it, so you need to choose one. You need to know what the bytes mean, and then convert them into whatever representation that you need. It is unfortunate that you’ve been downvoted for asking a question.

McWobbleston 7y ago

I'm well versed in Rust but I think you might need to use str::from_utf8(result.as_slice()) https://docs.rs/generic-array/0.8.2/generic_array/struct.GenericArray.html#method.as_slice https://docs.rs/generic-array/0.8.2/generic_array/struct.Gen... https://doc.rust-lang.org/std/str/fn.from_utf8.html https://doc.rust-lang.org/std/str/fn.from_utf8.html

kam 7y ago
That would be correct if the bytes were a string encoded in utf-8, but that's probably not the case for the output of a hash function.

unionpivo 7y ago

since we know that Sha256::new() will always produce 'valid' characters for utf8 you can just do let my_rust_string = str::from_utf8(result).unwarp() If there is a possibility of an error, (you read it from file, network ...) you can do: let my_rust_string = match str::from_utf8(result) { Ok(str) => str, Err(err) => panic!("Invalid utf8: {}", err), }; Or you can do lossy conversion (will have that question mark on chars that it cant decode) let my_rust_string = String::from_utf8_lossy(result); edit: Ok so i read sha2 api wrong. result() is raw bytes and result_str() is hex encoded string. Above wont be much use for either. And others have already explained what to use. I just stared programming in rust several months ago, and that was my pain also, since where i live we still have some other encoding in use.

the8472 7y ago

This seems to be a conceptual mistake that often happens when coming from high level languages, I have seen similar confusion on stack overflow relating to packet based network protocols. What many low-level data formats deal with are raw bytes ("byte strings" in some contexts). The output of a hasher is random binary data. What most humans are accustomed to are some form of encoding that makes it easier to spell out the octets. Hex and base64 are common. But they are not the native representation that the machine deals with. With almost everything being explicit in rust you need an explicit conversion from bytes to hex, base64, urlencode or some other format. Those conversion methods (with their contract often expressed as a separate trait) may be provided by the same crate or you may have to pull them in from a different crate. A hasher does not need to provide this itself because its output types can be enhanced by foreign traits.