diff --git a/src/dc_array.rs b/src/dc_array.rs
index 3ef41e7a0..16fc163ab 100644
--- a/src/dc_array.rs
+++ b/src/dc_array.rs
@@ -358,65 +358,46 @@ pub unsafe fn dc_array_get_string(
     array: *const dc_array_t,
     sep: *const libc::c_char,
 ) -> *mut libc::c_char {
-    let ret: *mut libc::c_char;
     if array.is_null() || (*array).magic != 0xa11aai32 as libc::c_uint || sep.is_null() {
         return dc_strdup(b"\x00" as *const u8 as *const libc::c_char);
     }
-    let mut i = 0;
-    ret = malloc(
-        (*array)
-            .count
-            .wrapping_mul((11usize).wrapping_add(strlen(sep)))
-            .wrapping_add(1),
-    ) as *mut libc::c_char;
-    if ret.is_null() {
-        exit(35i32);
-    }
-    *ret.offset(0isize) = 0i32 as libc::c_char;
-    while i < (*array).count {
-        if 0 != i {
-            strcat(ret, sep);
-        }
-        sprintf(
-            &mut *ret.offset(strlen(ret) as isize) as *mut libc::c_char,
-            b"%lu\x00" as *const u8 as *const libc::c_char,
-            *(*array).array.offset(i as isize) as libc::c_ulong,
-        );
-        i += 1
-    }
+    let cnt = (*array).count as usize;
+    let slice = std::slice::from_raw_parts((*array).array, cnt);
+    let sep = to_str(sep);
 
-    ret
+    let res = slice
+        .iter()
+        .enumerate()
+        .fold(String::with_capacity(2 * cnt), |mut res, (i, n)| {
+            if i == 0 {
+                res += &n.to_string();
+            } else {
+                res += sep;
+                res += &n.to_string();
+            }
+            res
+        });
+    strdup(to_cstring(res).as_ptr())
 }
 
+/// return comma-separated value-string from integer array
 pub unsafe fn dc_arr_to_string(arr: *const uint32_t, cnt: libc::c_int) -> *mut libc::c_char {
-    /* return comma-separated value-string from integer array */
-    let ret: *mut libc::c_char;
-    let sep: *const libc::c_char = b",\x00" as *const u8 as *const libc::c_char;
-    if arr.is_null() || cnt <= 0i32 {
+    if arr.is_null() || cnt == 0 {
         return dc_strdup(b"\x00" as *const u8 as *const libc::c_char);
     }
-    let mut i: libc::c_int;
-    ret = malloc(
-        (cnt as usize)
-            .wrapping_mul((11usize).wrapping_add(strlen(sep)))
-            .wrapping_add(0usize),
-    ) as *mut libc::c_char;
-    if ret.is_null() {
-        exit(35i32);
-    }
-    *ret.offset(0isize) = 0i32 as libc::c_char;
-    i = 0i32;
-    while i < cnt {
-        if 0 != i {
-            strcat(ret, sep);
-        }
-        sprintf(
-            &mut *ret.offset(strlen(ret) as isize) as *mut libc::c_char,
-            b"%lu\x00" as *const u8 as *const libc::c_char,
-            *arr.offset(i as isize) as libc::c_ulong,
-        );
-        i += 1
-    }
 
-    ret
+    let slice = std::slice::from_raw_parts(arr, cnt as usize);
+    let res = slice.iter().enumerate().fold(
+        String::with_capacity(2 * cnt as usize),
+        |mut res, (i, n)| {
+            if i == 0 {
+                res += &n.to_string();
+            } else {
+                res += ",";
+                res += &n.to_string();
+            }
+            res
+        },
+    );
+    strdup(to_cstring(res).as_ptr())
 }
diff --git a/src/dc_receive_imf.rs b/src/dc_receive_imf.rs
index 24fefd7c3..de4670e36 100644
--- a/src/dc_receive_imf.rs
+++ b/src/dc_receive_imf.rs
@@ -5,6 +5,7 @@ use mmime::mailmime_content::*;
 use mmime::mailmime_types::*;
 use mmime::mmapstring::*;
 use mmime::other::*;
+use sha2::{Digest, Sha256};
 
 use crate::constants::*;
 use crate::context::Context;
@@ -25,7 +26,6 @@ use crate::dc_strbuilder::*;
 use crate::dc_strencode::*;
 use crate::dc_tools::*;
 use crate::peerstate::*;
-use crate::pgp::dc_hash_sha256;
 use crate::types::*;
 use crate::x::*;
 
@@ -1694,7 +1694,6 @@ unsafe fn create_adhoc_grp_id(context: &Context, member_ids: *mut dc_array_t) ->
     let mut addr: *mut libc::c_char;
     let mut i: libc::c_int;
     let iCnt: libc::c_int;
-    let mut ret: *mut libc::c_char = 0 as *mut libc::c_char;
     let mut member_cs: dc_strbuilder_t = dc_strbuilder_t {
         buf: 0 as *mut libc::c_char,
         allocated: 0,
@@ -1734,34 +1733,31 @@ unsafe fn create_adhoc_grp_id(context: &Context, member_ids: *mut dc_array_t) ->
         );
         i += 1
     }
-    /* make sha-256 from the string */
-    let (binary_hash, binary_hash_len) = dc_hash_sha256(
-        member_cs.buf as *const uint8_t,
-        strlen(member_cs.buf) as usize,
-    );
-    if !binary_hash.is_null() {
-        ret = calloc(1, 256) as *mut libc::c_char;
-        if !ret.is_null() {
-            i = 0;
-            while i < 8 {
-                sprintf(
-                    &mut *ret.offset((i * 2i32) as isize) as *mut libc::c_char,
-                    b"%02x\x00" as *const u8 as *const libc::c_char,
-                    *binary_hash.offset(i as isize) as libc::c_int,
-                );
-                i += 1
-            }
-            let _v = Vec::from_raw_parts(binary_hash, binary_hash_len, binary_hash_len);
-        }
-    }
+
+    let ret = hex_hash(member_cs.buf as *const _, strlen(member_cs.buf));
     dc_array_free_ptr(member_addrs);
     dc_array_unref(member_addrs);
     free(member_ids_str as *mut libc::c_void);
     sqlite3_finalize(stmt);
     sqlite3_free(q3 as *mut libc::c_void);
     free(member_cs.buf as *mut libc::c_void);
-    return ret;
+
+    ret as *mut _
 }
+
+fn hex_hash(bytes_ptr: *const u8, bytes_len: libc::size_t) -> *const libc::c_char {
+    if bytes_ptr.is_null() || bytes_len == 0 {
+        return std::ptr::null();
+    }
+
+    let bytes = unsafe { std::slice::from_raw_parts(bytes_ptr, bytes_len) };
+    let result = Sha256::digest(bytes);
+    let result_hex = hex::encode(&result[..8]);
+    let result_cstring = to_cstring(result_hex);
+
+    unsafe { strdup(result_cstring.as_ptr()) }
+}
+
 unsafe fn search_chat_ids_by_contact_ids(
     context: &Context,
     unsorted_contact_ids: *const dc_array_t,
@@ -2299,3 +2295,17 @@ unsafe fn add_or_lookup_contact_by_addr(
         }
     };
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_hex_hash() {
+        let data = b"hello world\x00" as *const u8 as *const libc::c_char;
+
+        let res_c = hex_hash(data as *const _, unsafe { strlen(data) });
+        let res = to_string(res_c);
+        assert_eq!(res, "b94d27b9934d3e08");
+    }
+}
diff --git a/src/pgp.rs b/src/pgp.rs
index 423ac0f3d..e66f0197a 100644
--- a/src/pgp.rs
+++ b/src/pgp.rs
@@ -10,7 +10,6 @@ use pgp::composed::{
 use pgp::crypto::{HashAlgorithm, SymmetricKeyAlgorithm};
 use pgp::types::{CompressionAlgorithm, KeyTrait, SecretKeyTrait, StringToKey};
 use rand::thread_rng;
-use sha2::{Digest, Sha256};
 
 use crate::dc_tools::*;
 use crate::key::*;
@@ -329,21 +328,3 @@ pub fn dc_pgp_symm_decrypt(
         .ok()
         .and_then(|content| content)
 }
-
-/// Calculate the SHA256 hash of the given bytes.
-pub fn dc_hash_sha256(bytes_ptr: *const u8, bytes_len: libc::size_t) -> (*mut u8, libc::size_t) {
-    assert!(!bytes_ptr.is_null());
-    assert!(bytes_len > 0);
-
-    let bytes = unsafe { std::slice::from_raw_parts(bytes_ptr, bytes_len) };
-    let result = Sha256::digest(bytes);
-
-    let mut r = result.to_vec();
-    r.shrink_to_fit();
-
-    let ptr = r.as_ptr();
-    let len = r.len();
-    std::mem::forget(r);
-
-    (ptr as *mut _, len)
-}
diff --git a/src/x.rs b/src/x.rs
index ebaa91913..51cff4ddc 100644
--- a/src/x.rs
+++ b/src/x.rs
@@ -4,8 +4,8 @@ use crate::types::*;
 pub use libc::{
     atoi, calloc, close, closedir, exit, fclose, fgets, fopen, fread, free, fseek, ftell, fwrite,
     malloc, memcmp, memcpy, memmove, memset, mkdir, open, opendir, printf, read, readdir, realloc,
-    remove, sprintf, strcat, strchr, strcmp, strcpy, strcspn, strlen, strncmp, strncpy, strrchr,
-    strspn, strstr, strtol, system, tolower, write,
+    remove, strcat, strchr, strcmp, strcpy, strcspn, strlen, strncmp, strncpy, strrchr, strspn,
+    strstr, strtol, system, tolower, write,
 };
 
 pub unsafe fn strdup(s: *const libc::c_char) -> *mut libc::c_char {
diff --git a/tests/stress.rs b/tests/stress.rs
index 8ab4f463f..213ea2156 100644
--- a/tests/stress.rs
+++ b/tests/stress.rs
@@ -810,8 +810,7 @@ unsafe fn stress_functions(context: &Context) {
                          as *const u8 as *const libc::c_char);
     } else {
     };
-    let mut str_0: *mut libc::c_char =
-        dc_array_get_string(arr, b"-\x00" as *const u8 as *const libc::c_char);
+    let str_0 = dc_array_get_string(arr, b"-\x00" as *const u8 as *const libc::c_char);
     if 0 != !(strcmp(
         str_0,
         b"0-7-13-666-5000\x00" as *const u8 as *const libc::c_char,
@@ -827,28 +826,6 @@ unsafe fn stress_functions(context: &Context) {
     } else {
     };
     free(str_0 as *mut libc::c_void);
-    let arr2: [uint32_t; 4] = [
-        0i32 as uint32_t,
-        12i32 as uint32_t,
-        133i32 as uint32_t,
-        1999999i32 as uint32_t,
-    ];
-    str_0 = dc_arr_to_string(arr2.as_ptr(), 4i32);
-    if 0 != !(strcmp(
-        str_0,
-        b"0,12,133,1999999\x00" as *const u8 as *const libc::c_char,
-    ) == 0i32) as usize
-    {
-        __assert_rtn(
-            (*::std::mem::transmute::<&[u8; 17], &[libc::c_char; 17]>(b"stress_functions\x00"))
-                .as_ptr(),
-            b"../cmdline/stress.c\x00" as *const u8 as *const libc::c_char,
-            665i32,
-            b"strcmp(str, \"0,12,133,1999999\")==0\x00" as *const u8 as *const libc::c_char,
-        );
-    } else {
-    };
-    free(str_0 as *mut libc::c_void);
     dc_array_empty(arr);
     dc_array_add_ptr(
         arr,
@@ -2549,3 +2526,17 @@ fn test_stress_tests() {
         stress_functions(&context.ctx);
     }
 }
+
+#[test]
+fn test_arr_to_string() {
+    let arr2: [uint32_t; 4] = [
+        0i32 as uint32_t,
+        12i32 as uint32_t,
+        133i32 as uint32_t,
+        1999999i32 as uint32_t,
+    ];
+
+    let str_0 = unsafe { dc_arr_to_string(arr2.as_ptr(), 4i32) };
+    assert_eq!(to_string(str_0), "0,12,133,1999999");
+    unsafe { free(str_0 as *mut _) };
+}