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lbeder · Jun 23, 2023 · 48b514c · 48b514c
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diff --git a/README.md b/README.md
@@ -23,16 +23,16 @@ Options:
 ### Deriving
 
 ```sh
-Derive a value using Scrypt KDF
+Derive a key using Scrypt KDF
 
-Usage: scrypt-kdf derive --iterations <ITERATIONS> --log-n <LOG_N> --r <R> --p <P> --l <L>
+Usage: scrypt-kdf derive [OPTIONS]
 
 Options:
-  -i, --iterations <ITERATIONS>  Number of iterations [default: 100]
-  -l, --log-n <LOG_N>            Work factor [default: 20]
-  -r, --r <R>                    Block size [default: 8]
-  -p, --p <P>                    Parallelization parameter [default: 1]
-  -l, --l <L>                    Length of the derived result [default: 16]
+  -i, --iterations <ITERATIONS>  Number of iterations (must be greater than 0 and less than or equal to 4294967295) [default: 100]
+  -n <LOG_N>                     CPU/memory cost parameter (must be less than 64) [default: 20]
+  -r <R>                         Block size parameter, which fine-tunes sequential memory read size and performance (must be greater than 0 and less than or equal to 4294967295) [default: 8]
+  -p <P>                         Parallelization parameter (must be greater than 0 and less than 4294967295) [default: 1]
+  -l, --length <LENGTH>          Length of the derived result (must be greater than 9 and less than or equal to 64) [default: 16]
   -h, --help                     Print help
 ```
 

diff --git a/src/main.rs b/src/main.rs
@@ -17,7 +17,7 @@ use crossterm::{
 };
 use humantime::format_duration;
 use pbr::ProgressBar;
-use scrypt_kdf::DEFAULT_SCRYPT_KDF_OPTIONS;
+use scrypt_kdf::{DEFAULT_SCRYPT_KDF_OPTIONS, MAX_KDF_LEN, MIN_KDF_LEN};
 use std::{
     env,
     io::{self, Write},
@@ -36,22 +36,22 @@ struct Cli {
 
 #[derive(Subcommand)]
 enum Commands {
-    #[command(about = "Derive a value using Scrypt KDF")]
+    #[command(about = "Derive a key using Scrypt KDF")]
     Derive {
-        #[arg(short, long, default_value = DEFAULT_SCRYPT_KDF_OPTIONS.iterations.to_string(), help = "Number of iterations")]
+        #[arg(short, long, default_value = DEFAULT_SCRYPT_KDF_OPTIONS.iterations.to_string(), help = format!("Number of iterations (must be greater than 0 and less than or equal to {})", u32::MAX))]
         iterations: u32,
 
-        #[arg(short, long, default_value = DEFAULT_SCRYPT_KDF_OPTIONS.log_n.to_string(), help = "Work factor")]
+        #[arg(short = 'n', default_value = DEFAULT_SCRYPT_KDF_OPTIONS.log_n.to_string(), help = format!("CPU/memory cost parameter (must be less than {})", usize::BITS))]
         log_n: u8,
 
-        #[arg(short, long, default_value = DEFAULT_SCRYPT_KDF_OPTIONS.r.to_string(), help = "Block size")]
+        #[arg(short, default_value = DEFAULT_SCRYPT_KDF_OPTIONS.r.to_string(), help = format!("Block size parameter, which fine-tunes sequential memory read size and performance (must be greater than 0 and less than or equal to {})", u32::MAX))]
         r: u32,
 
-        #[arg(short, long, default_value = DEFAULT_SCRYPT_KDF_OPTIONS.p.to_string(), help = "Parallelization parameter")]
+        #[arg(short, default_value = DEFAULT_SCRYPT_KDF_OPTIONS.p.to_string(), help = format!("Parallelization parameter (must be greater than 0 and less than {})", u32::MAX))]
         p: u32,
 
-        #[arg(short, long, default_value = DEFAULT_SCRYPT_KDF_OPTIONS.len.to_string(), help = "Length of the derived result")]
-        l: usize,
+        #[arg(short, long, default_value = DEFAULT_SCRYPT_KDF_OPTIONS.len.to_string(), help = format!("Length of the derived result (must be greater than {} and less than or equal to {})", MIN_KDF_LEN - 1, MAX_KDF_LEN))]
+        length: u8,
     },
 
     #[command(about = "Print test vectors")]
@@ -111,15 +111,15 @@ fn main() {
             log_n,
             r,
             p,
-            l,
+            length,
         }) => {
             println!(
                 "Parameters: {} (log_n: {}, r: {}, p: {}, len: {})\n",
                 "Scrypt".yellow(),
                 log_n.to_string().cyan(),
                 r.to_string().cyan(),
                 p.to_string().cyan(),
-                l.to_string().cyan(),
+                length.to_string().cyan(),
             );
 
             let salt = get_salt();
@@ -136,7 +136,7 @@ fn main() {
                 log_n: *log_n,
                 r: *r,
                 p: *p,
-                len: *l,
+                len: *length,
                 iterations: *iterations,
             };
             let kdf = ScryptKDF::new(&opts);

diff --git a/src/scrypt_kdf.rs b/src/scrypt_kdf.rs
@@ -6,7 +6,7 @@ pub struct ScryptKDFOptions {
     pub r: u32,
     pub p: u32,
     pub iterations: u32,
-    pub len: usize,
+    pub len: u8,
 }
 
 #[derive(PartialEq, Debug)]
@@ -49,14 +49,19 @@ pub const TEST_VECTORS: &[&TestScryptKDFOptions] = &[
     },
 ];
 
-pub const MAX_KDF_LEN: usize = 64;
+pub const MIN_KDF_LEN: u8 = 10;
+pub const MAX_KDF_LEN: u8 = 64;
 
 pub struct ScryptKDF<'a> {
     opts: &'a ScryptKDFOptions,
 }
 
 impl<'a> ScryptKDF<'a> {
     pub fn new(opts: &'a ScryptKDFOptions) -> Self {
+        if opts.len < MIN_KDF_LEN {
+            panic!("length {} is lower than the min length of {MIN_KDF_LEN}", opts.len);
+        }
+
         if opts.len > MAX_KDF_LEN {
             panic!("length {} is greater than the max length of {MAX_KDF_LEN}", opts.len);
         }
@@ -65,7 +70,7 @@ impl<'a> ScryptKDF<'a> {
     }
 
     fn derive(&self, salt: &[u8], secret: &[u8]) -> Vec<u8> {
-        let mut dk = vec![0; self.opts.len];
+        let mut dk = vec![0; self.opts.len as usize];
 
         scrypt(
             secret,