diff --git a/src/Principal.mo b/src/Principal.mo
index d157df47..d1f1d2db 100644
--- a/src/Principal.mo
+++ b/src/Principal.mo
@@ -27,6 +27,12 @@
 import Prim "mo:⛔";
 import Blob "Blob";
 import Hash "Hash";
+import Array "Array";
+import Nat8 "Nat8";
+import Nat32 "Nat32";
+import Nat64 "Nat64";
+import Text "Text";
+
 module {
 
   public type Principal = Prim.Types.Principal;
@@ -43,6 +49,37 @@ module {
   /// ```
   public func fromActor(a : actor {}) : Principal = Prim.principalOfActor a;
 
+  /// Compute the Ledger account identifier of a principal. Optionally specify a sub-account.
+  ///
+  /// Example:
+  /// ```motoko include=import
+  /// let principal = Principal.fromText("un4fu-tqaaa-aaaab-qadjq-cai");
+  /// let subAccount : Blob = "\4A\8D\3F\2B\6E\01\C8\7D\9E\03\B4\56\7C\F8\9A\01\D2\34\56\78\9A\BC\DE\F0\12\34\56\78\9A\BC\DE\F0";
+  /// let account = Principal.toLedgerAccount(principal, ?subAccount); // => \8C\5C\20\C6\15\3F\7F\51\E2\0D\0F\0F\B5\08\51\5B\47\65\63\A9\62\B4\A9\91\5F\4F\02\70\8A\ED\4F\82
+  /// ```
+  public func toLedgerAccount(principal : Principal, subAccount : ?Blob) : Blob {
+    let sha224 = SHA224();
+    let accountSeparator : Blob = "\0Aaccount-id";
+    sha224.writeBlob(accountSeparator);
+    sha224.writeBlob(toBlob(principal));
+    switch subAccount {
+      case (?subAccount) {
+        sha224.writeBlob(subAccount)
+      };
+      case (null) {
+        let defaultSubAccount = Array.tabulate<Nat8>(32, func _ = 0);
+        sha224.writeArray(defaultSubAccount)
+      }
+    };
+
+    let hashSum = sha224.sum();
+
+    // hashBlob is a CRC32 implementation
+    let crc32Bytes = nat32ToByteArray(Prim.hashBlob hashSum);
+
+    Blob.fromArray(Array.append(crc32Bytes, Blob.toArray(hashSum)))
+  };
+
   /// Convert a `Principal` to its `Blob` (bytes) representation.
   ///
   /// Example:
@@ -254,5 +291,932 @@ module {
   /// as a function value at the moment.
   public func greaterOrEqual(principal1 : Principal, principal2 : Principal) : Bool {
     principal1 >= principal2
+  };
+
+  /**
+  * SHA224 Utilities used in toAccount().
+  * Utilities are not exposed as public functions.
+  * Taken with permission from https://github.com/research-ag/sha2
+  **/
+  let K00 : Nat32 = 0x428a2f98;
+  let K01 : Nat32 = 0x71374491;
+  let K02 : Nat32 = 0xb5c0fbcf;
+  let K03 : Nat32 = 0xe9b5dba5;
+  let K04 : Nat32 = 0x3956c25b;
+  let K05 : Nat32 = 0x59f111f1;
+  let K06 : Nat32 = 0x923f82a4;
+  let K07 : Nat32 = 0xab1c5ed5;
+  let K08 : Nat32 = 0xd807aa98;
+  let K09 : Nat32 = 0x12835b01;
+  let K10 : Nat32 = 0x243185be;
+  let K11 : Nat32 = 0x550c7dc3;
+  let K12 : Nat32 = 0x72be5d74;
+  let K13 : Nat32 = 0x80deb1fe;
+  let K14 : Nat32 = 0x9bdc06a7;
+  let K15 : Nat32 = 0xc19bf174;
+  let K16 : Nat32 = 0xe49b69c1;
+  let K17 : Nat32 = 0xefbe4786;
+  let K18 : Nat32 = 0x0fc19dc6;
+  let K19 : Nat32 = 0x240ca1cc;
+  let K20 : Nat32 = 0x2de92c6f;
+  let K21 : Nat32 = 0x4a7484aa;
+  let K22 : Nat32 = 0x5cb0a9dc;
+  let K23 : Nat32 = 0x76f988da;
+  let K24 : Nat32 = 0x983e5152;
+  let K25 : Nat32 = 0xa831c66d;
+  let K26 : Nat32 = 0xb00327c8;
+  let K27 : Nat32 = 0xbf597fc7;
+  let K28 : Nat32 = 0xc6e00bf3;
+  let K29 : Nat32 = 0xd5a79147;
+  let K30 : Nat32 = 0x06ca6351;
+  let K31 : Nat32 = 0x14292967;
+  let K32 : Nat32 = 0x27b70a85;
+  let K33 : Nat32 = 0x2e1b2138;
+  let K34 : Nat32 = 0x4d2c6dfc;
+  let K35 : Nat32 = 0x53380d13;
+  let K36 : Nat32 = 0x650a7354;
+  let K37 : Nat32 = 0x766a0abb;
+  let K38 : Nat32 = 0x81c2c92e;
+  let K39 : Nat32 = 0x92722c85;
+  let K40 : Nat32 = 0xa2bfe8a1;
+  let K41 : Nat32 = 0xa81a664b;
+  let K42 : Nat32 = 0xc24b8b70;
+  let K43 : Nat32 = 0xc76c51a3;
+  let K44 : Nat32 = 0xd192e819;
+  let K45 : Nat32 = 0xd6990624;
+  let K46 : Nat32 = 0xf40e3585;
+  let K47 : Nat32 = 0x106aa070;
+  let K48 : Nat32 = 0x19a4c116;
+  let K49 : Nat32 = 0x1e376c08;
+  let K50 : Nat32 = 0x2748774c;
+  let K51 : Nat32 = 0x34b0bcb5;
+  let K52 : Nat32 = 0x391c0cb3;
+  let K53 : Nat32 = 0x4ed8aa4a;
+  let K54 : Nat32 = 0x5b9cca4f;
+  let K55 : Nat32 = 0x682e6ff3;
+  let K56 : Nat32 = 0x748f82ee;
+  let K57 : Nat32 = 0x78a5636f;
+  let K58 : Nat32 = 0x84c87814;
+  let K59 : Nat32 = 0x8cc70208;
+  let K60 : Nat32 = 0x90befffa;
+  let K61 : Nat32 = 0xa4506ceb;
+  let K62 : Nat32 = 0xbef9a3f7;
+  let K63 : Nat32 = 0xc67178f2;
+
+  let ivs : [[Nat32]] = [
+    [
+      // 224
+      0xc1059ed8,
+      0x367cd507,
+      0x3070dd17,
+      0xf70e5939,
+      0xffc00b31,
+      0x68581511,
+      0x64f98fa7,
+      0xbefa4fa4
+    ],
+    [
+      // 256
+      0x6a09e667,
+      0xbb67ae85,
+      0x3c6ef372,
+      0xa54ff53a,
+      0x510e527f,
+      0x9b05688c,
+      0x1f83d9ab,
+      0x5be0cd19
+    ]
+  ];
+
+  let rot = Nat32.bitrotRight;
+
+  class SHA224() {
+    let (sum_bytes, iv) = (28, 0);
+
+    var s0 : Nat32 = 0;
+    var s1 : Nat32 = 0;
+    var s2 : Nat32 = 0;
+    var s3 : Nat32 = 0;
+    var s4 : Nat32 = 0;
+    var s5 : Nat32 = 0;
+    var s6 : Nat32 = 0;
+    var s7 : Nat32 = 0;
+
+    let msg : [var Nat32] = Array.init<Nat32>(16, 0);
+    let digest = Array.init<Nat8>(sum_bytes, 0);
+    var word : Nat32 = 0;
+
+    var i_msg : Nat8 = 0;
+    var i_byte : Nat8 = 4;
+    var i_block : Nat64 = 0;
+
+    public func reset() {
+      i_msg := 0;
+      i_byte := 4;
+      i_block := 0;
+      s0 := ivs[iv][0];
+      s1 := ivs[iv][1];
+      s2 := ivs[iv][2];
+      s3 := ivs[iv][3];
+      s4 := ivs[iv][4];
+      s5 := ivs[iv][5];
+      s6 := ivs[iv][6];
+      s7 := ivs[iv][7]
+    };
+
+    reset();
+
+    private func writeByte(val : Nat8) : () {
+      word := (word << 8) ^ Nat32.fromIntWrap(Nat8.toNat(val));
+      i_byte -%= 1;
+      if (i_byte == 0) {
+        msg[Nat8.toNat(i_msg)] := word;
+        word := 0;
+        i_byte := 4;
+        i_msg +%= 1;
+        if (i_msg == 16) {
+          process_block();
+          i_msg := 0;
+          i_block +%= 1
+        }
+      }
+    };
+
+    private func process_block() : () {
+      let w00 = msg[0];
+      let w01 = msg[1];
+      let w02 = msg[2];
+      let w03 = msg[3];
+      let w04 = msg[4];
+      let w05 = msg[5];
+      let w06 = msg[6];
+      let w07 = msg[7];
+      let w08 = msg[8];
+      let w09 = msg[9];
+      let w10 = msg[10];
+      let w11 = msg[11];
+      let w12 = msg[12];
+      let w13 = msg[13];
+      let w14 = msg[14];
+      let w15 = msg[15];
+      let w16 = w00 +% rot(w01, 07) ^ rot(w01, 18) ^ (w01 >> 03) +% w09 +% rot(w14, 17) ^ rot(w14, 19) ^ (w14 >> 10);
+      let w17 = w01 +% rot(w02, 07) ^ rot(w02, 18) ^ (w02 >> 03) +% w10 +% rot(w15, 17) ^ rot(w15, 19) ^ (w15 >> 10);
+      let w18 = w02 +% rot(w03, 07) ^ rot(w03, 18) ^ (w03 >> 03) +% w11 +% rot(w16, 17) ^ rot(w16, 19) ^ (w16 >> 10);
+      let w19 = w03 +% rot(w04, 07) ^ rot(w04, 18) ^ (w04 >> 03) +% w12 +% rot(w17, 17) ^ rot(w17, 19) ^ (w17 >> 10);
+      let w20 = w04 +% rot(w05, 07) ^ rot(w05, 18) ^ (w05 >> 03) +% w13 +% rot(w18, 17) ^ rot(w18, 19) ^ (w18 >> 10);
+      let w21 = w05 +% rot(w06, 07) ^ rot(w06, 18) ^ (w06 >> 03) +% w14 +% rot(w19, 17) ^ rot(w19, 19) ^ (w19 >> 10);
+      let w22 = w06 +% rot(w07, 07) ^ rot(w07, 18) ^ (w07 >> 03) +% w15 +% rot(w20, 17) ^ rot(w20, 19) ^ (w20 >> 10);
+      let w23 = w07 +% rot(w08, 07) ^ rot(w08, 18) ^ (w08 >> 03) +% w16 +% rot(w21, 17) ^ rot(w21, 19) ^ (w21 >> 10);
+      let w24 = w08 +% rot(w09, 07) ^ rot(w09, 18) ^ (w09 >> 03) +% w17 +% rot(w22, 17) ^ rot(w22, 19) ^ (w22 >> 10);
+      let w25 = w09 +% rot(w10, 07) ^ rot(w10, 18) ^ (w10 >> 03) +% w18 +% rot(w23, 17) ^ rot(w23, 19) ^ (w23 >> 10);
+      let w26 = w10 +% rot(w11, 07) ^ rot(w11, 18) ^ (w11 >> 03) +% w19 +% rot(w24, 17) ^ rot(w24, 19) ^ (w24 >> 10);
+      let w27 = w11 +% rot(w12, 07) ^ rot(w12, 18) ^ (w12 >> 03) +% w20 +% rot(w25, 17) ^ rot(w25, 19) ^ (w25 >> 10);
+      let w28 = w12 +% rot(w13, 07) ^ rot(w13, 18) ^ (w13 >> 03) +% w21 +% rot(w26, 17) ^ rot(w26, 19) ^ (w26 >> 10);
+      let w29 = w13 +% rot(w14, 07) ^ rot(w14, 18) ^ (w14 >> 03) +% w22 +% rot(w27, 17) ^ rot(w27, 19) ^ (w27 >> 10);
+      let w30 = w14 +% rot(w15, 07) ^ rot(w15, 18) ^ (w15 >> 03) +% w23 +% rot(w28, 17) ^ rot(w28, 19) ^ (w28 >> 10);
+      let w31 = w15 +% rot(w16, 07) ^ rot(w16, 18) ^ (w16 >> 03) +% w24 +% rot(w29, 17) ^ rot(w29, 19) ^ (w29 >> 10);
+      let w32 = w16 +% rot(w17, 07) ^ rot(w17, 18) ^ (w17 >> 03) +% w25 +% rot(w30, 17) ^ rot(w30, 19) ^ (w30 >> 10);
+      let w33 = w17 +% rot(w18, 07) ^ rot(w18, 18) ^ (w18 >> 03) +% w26 +% rot(w31, 17) ^ rot(w31, 19) ^ (w31 >> 10);
+      let w34 = w18 +% rot(w19, 07) ^ rot(w19, 18) ^ (w19 >> 03) +% w27 +% rot(w32, 17) ^ rot(w32, 19) ^ (w32 >> 10);
+      let w35 = w19 +% rot(w20, 07) ^ rot(w20, 18) ^ (w20 >> 03) +% w28 +% rot(w33, 17) ^ rot(w33, 19) ^ (w33 >> 10);
+      let w36 = w20 +% rot(w21, 07) ^ rot(w21, 18) ^ (w21 >> 03) +% w29 +% rot(w34, 17) ^ rot(w34, 19) ^ (w34 >> 10);
+      let w37 = w21 +% rot(w22, 07) ^ rot(w22, 18) ^ (w22 >> 03) +% w30 +% rot(w35, 17) ^ rot(w35, 19) ^ (w35 >> 10);
+      let w38 = w22 +% rot(w23, 07) ^ rot(w23, 18) ^ (w23 >> 03) +% w31 +% rot(w36, 17) ^ rot(w36, 19) ^ (w36 >> 10);
+      let w39 = w23 +% rot(w24, 07) ^ rot(w24, 18) ^ (w24 >> 03) +% w32 +% rot(w37, 17) ^ rot(w37, 19) ^ (w37 >> 10);
+      let w40 = w24 +% rot(w25, 07) ^ rot(w25, 18) ^ (w25 >> 03) +% w33 +% rot(w38, 17) ^ rot(w38, 19) ^ (w38 >> 10);
+      let w41 = w25 +% rot(w26, 07) ^ rot(w26, 18) ^ (w26 >> 03) +% w34 +% rot(w39, 17) ^ rot(w39, 19) ^ (w39 >> 10);
+      let w42 = w26 +% rot(w27, 07) ^ rot(w27, 18) ^ (w27 >> 03) +% w35 +% rot(w40, 17) ^ rot(w40, 19) ^ (w40 >> 10);
+      let w43 = w27 +% rot(w28, 07) ^ rot(w28, 18) ^ (w28 >> 03) +% w36 +% rot(w41, 17) ^ rot(w41, 19) ^ (w41 >> 10);
+      let w44 = w28 +% rot(w29, 07) ^ rot(w29, 18) ^ (w29 >> 03) +% w37 +% rot(w42, 17) ^ rot(w42, 19) ^ (w42 >> 10);
+      let w45 = w29 +% rot(w30, 07) ^ rot(w30, 18) ^ (w30 >> 03) +% w38 +% rot(w43, 17) ^ rot(w43, 19) ^ (w43 >> 10);
+      let w46 = w30 +% rot(w31, 07) ^ rot(w31, 18) ^ (w31 >> 03) +% w39 +% rot(w44, 17) ^ rot(w44, 19) ^ (w44 >> 10);
+      let w47 = w31 +% rot(w32, 07) ^ rot(w32, 18) ^ (w32 >> 03) +% w40 +% rot(w45, 17) ^ rot(w45, 19) ^ (w45 >> 10);
+      let w48 = w32 +% rot(w33, 07) ^ rot(w33, 18) ^ (w33 >> 03) +% w41 +% rot(w46, 17) ^ rot(w46, 19) ^ (w46 >> 10);
+      let w49 = w33 +% rot(w34, 07) ^ rot(w34, 18) ^ (w34 >> 03) +% w42 +% rot(w47, 17) ^ rot(w47, 19) ^ (w47 >> 10);
+      let w50 = w34 +% rot(w35, 07) ^ rot(w35, 18) ^ (w35 >> 03) +% w43 +% rot(w48, 17) ^ rot(w48, 19) ^ (w48 >> 10);
+      let w51 = w35 +% rot(w36, 07) ^ rot(w36, 18) ^ (w36 >> 03) +% w44 +% rot(w49, 17) ^ rot(w49, 19) ^ (w49 >> 10);
+      let w52 = w36 +% rot(w37, 07) ^ rot(w37, 18) ^ (w37 >> 03) +% w45 +% rot(w50, 17) ^ rot(w50, 19) ^ (w50 >> 10);
+      let w53 = w37 +% rot(w38, 07) ^ rot(w38, 18) ^ (w38 >> 03) +% w46 +% rot(w51, 17) ^ rot(w51, 19) ^ (w51 >> 10);
+      let w54 = w38 +% rot(w39, 07) ^ rot(w39, 18) ^ (w39 >> 03) +% w47 +% rot(w52, 17) ^ rot(w52, 19) ^ (w52 >> 10);
+      let w55 = w39 +% rot(w40, 07) ^ rot(w40, 18) ^ (w40 >> 03) +% w48 +% rot(w53, 17) ^ rot(w53, 19) ^ (w53 >> 10);
+      let w56 = w40 +% rot(w41, 07) ^ rot(w41, 18) ^ (w41 >> 03) +% w49 +% rot(w54, 17) ^ rot(w54, 19) ^ (w54 >> 10);
+      let w57 = w41 +% rot(w42, 07) ^ rot(w42, 18) ^ (w42 >> 03) +% w50 +% rot(w55, 17) ^ rot(w55, 19) ^ (w55 >> 10);
+      let w58 = w42 +% rot(w43, 07) ^ rot(w43, 18) ^ (w43 >> 03) +% w51 +% rot(w56, 17) ^ rot(w56, 19) ^ (w56 >> 10);
+      let w59 = w43 +% rot(w44, 07) ^ rot(w44, 18) ^ (w44 >> 03) +% w52 +% rot(w57, 17) ^ rot(w57, 19) ^ (w57 >> 10);
+      let w60 = w44 +% rot(w45, 07) ^ rot(w45, 18) ^ (w45 >> 03) +% w53 +% rot(w58, 17) ^ rot(w58, 19) ^ (w58 >> 10);
+      let w61 = w45 +% rot(w46, 07) ^ rot(w46, 18) ^ (w46 >> 03) +% w54 +% rot(w59, 17) ^ rot(w59, 19) ^ (w59 >> 10);
+      let w62 = w46 +% rot(w47, 07) ^ rot(w47, 18) ^ (w47 >> 03) +% w55 +% rot(w60, 17) ^ rot(w60, 19) ^ (w60 >> 10);
+      let w63 = w47 +% rot(w48, 07) ^ rot(w48, 18) ^ (w48 >> 03) +% w56 +% rot(w61, 17) ^ rot(w61, 19) ^ (w61 >> 10);
+
+      /*
+      for ((i, j, k, l, m) in expansion_rounds.vals()) {
+        // (j,k,l,m) = (i+1,i+9,i+14,i+16)
+        let (v0, v1) = (msg[j], msg[l]);
+        let s0 = rot(v0, 07) ^ rot(v0, 18) ^ (v0 >> 03);
+        let s1 = rot(v1, 17) ^ rot(v1, 19) ^ (v1 >> 10);
+        msg[m] := msg[i] +% s0 +% msg[k] +% s1;
+      };
+      */
+      // compress
+      var a = s0;
+      var b = s1;
+      var c = s2;
+      var d = s3;
+      var e = s4;
+      var f = s5;
+      var g = s6;
+      var h = s7;
+      var t = 0 : Nat32;
+
+      t := h +% K00 +% w00 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K01 +% w01 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K02 +% w02 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K03 +% w03 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K04 +% w04 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K05 +% w05 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K06 +% w06 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K07 +% w07 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K08 +% w08 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K09 +% w09 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K10 +% w10 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K11 +% w11 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K12 +% w12 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K13 +% w13 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K14 +% w14 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K15 +% w15 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K16 +% w16 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K17 +% w17 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K18 +% w18 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K19 +% w19 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K20 +% w20 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K21 +% w21 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K22 +% w22 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K23 +% w23 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K24 +% w24 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K25 +% w25 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K26 +% w26 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K27 +% w27 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K28 +% w28 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K29 +% w29 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K30 +% w30 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K31 +% w31 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K32 +% w32 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K33 +% w33 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K34 +% w34 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K35 +% w35 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K36 +% w36 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K37 +% w37 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K38 +% w38 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K39 +% w39 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K40 +% w40 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K41 +% w41 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K42 +% w42 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K43 +% w43 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K44 +% w44 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K45 +% w45 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K46 +% w46 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K47 +% w47 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K48 +% w48 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K49 +% w49 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K50 +% w50 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K51 +% w51 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K52 +% w52 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K53 +% w53 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K54 +% w54 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K55 +% w55 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K56 +% w56 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K57 +% w57 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K58 +% w58 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K59 +% w59 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K60 +% w60 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K61 +% w61 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K62 +% w62 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+      t := h +% K63 +% w63 +% (e & f) ^ (^ e & g) +% rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+      h := g;
+      g := f;
+      f := e;
+      e := d +% t;
+      d := c;
+      c := b;
+      b := a;
+      a := t +% (b & c) ^ (b & d) ^ (c & d) +% rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+
+      /*
+      for (i in compression_rounds.keys()) {
+        let ch = (e & f) ^ (^ e & g);
+        let maj = (a & b) ^ (a & c) ^ (b & c);
+        let sigma0 = rot(a, 02) ^ rot(a, 13) ^ rot(a, 22);
+        let sigma1 = rot(e, 06) ^ rot(e, 11) ^ rot(e, 25);
+        let t = h +% K[i] +% msg[i] +% ch +% sigma1;
+        h := g;
+        g := f;
+        f := e;
+        e := d +% t;
+        d := c;
+        c := b;
+        b := a;
+        a := t +% maj +% sigma0;
+      };
+      */
+      // final addition
+      s0 +%= a;
+      s1 +%= b;
+      s2 +%= c;
+      s3 +%= d;
+      s4 +%= e;
+      s5 +%= f;
+      s6 +%= g;
+      s7 +%= h
+    };
+
+    public func writeIter(iter : { next() : ?Nat8 }) : () {
+      label reading loop {
+        switch (iter.next()) {
+          case (?val) {
+            writeByte(val);
+            continue reading
+          };
+          case (null) {
+            break reading
+          }
+        }
+      }
+    };
+
+    public func writeArray(arr : [Nat8]) : () = writeIter(arr.vals());
+    public func writeBlob(blob : Blob) : () = writeIter(blob.vals());
+
+    public func sum() : Blob {
+      // calculate padding
+      // t = bytes in the last incomplete block (0-63)
+      let t : Nat8 = (i_msg << 2) +% 4 -% i_byte;
+      // p = length of padding (1-64)
+      var p : Nat8 = if (t < 56) (56 -% t) else (120 -% t);
+      // n_bits = length of message in bits
+      let n_bits : Nat64 = ((i_block << 6) +% Nat64.fromIntWrap(Nat8.toNat(t))) << 3;
+
+      // write padding
+      writeByte(0x80);
+      p -%= 1;
+      while (p != 0) {
+        writeByte(0x00);
+        p -%= 1
+      };
+
+      // write length (8 bytes)
+      // Note: this exactly fills the block buffer, hence process_block will get
+      // triggered by the last writeByte
+      writeByte(Nat8.fromIntWrap(Nat64.toNat((n_bits >> 56) & 0xff)));
+      writeByte(Nat8.fromIntWrap(Nat64.toNat((n_bits >> 48) & 0xff)));
+      writeByte(Nat8.fromIntWrap(Nat64.toNat((n_bits >> 40) & 0xff)));
+      writeByte(Nat8.fromIntWrap(Nat64.toNat((n_bits >> 32) & 0xff)));
+      writeByte(Nat8.fromIntWrap(Nat64.toNat((n_bits >> 24) & 0xff)));
+      writeByte(Nat8.fromIntWrap(Nat64.toNat((n_bits >> 16) & 0xff)));
+      writeByte(Nat8.fromIntWrap(Nat64.toNat((n_bits >> 8) & 0xff)));
+      writeByte(Nat8.fromIntWrap(Nat64.toNat(n_bits & 0xff)));
+
+      // retrieve sum
+      digest[0] := Nat8.fromIntWrap(Nat32.toNat((s0 >> 24) & 0xff));
+      digest[1] := Nat8.fromIntWrap(Nat32.toNat((s0 >> 16) & 0xff));
+      digest[2] := Nat8.fromIntWrap(Nat32.toNat((s0 >> 8) & 0xff));
+      digest[3] := Nat8.fromIntWrap(Nat32.toNat(s0 & 0xff));
+      digest[4] := Nat8.fromIntWrap(Nat32.toNat((s1 >> 24) & 0xff));
+      digest[5] := Nat8.fromIntWrap(Nat32.toNat((s1 >> 16) & 0xff));
+      digest[6] := Nat8.fromIntWrap(Nat32.toNat((s1 >> 8) & 0xff));
+      digest[7] := Nat8.fromIntWrap(Nat32.toNat(s1 & 0xff));
+      digest[8] := Nat8.fromIntWrap(Nat32.toNat((s2 >> 24) & 0xff));
+      digest[9] := Nat8.fromIntWrap(Nat32.toNat((s2 >> 16) & 0xff));
+      digest[10] := Nat8.fromIntWrap(Nat32.toNat((s2 >> 8) & 0xff));
+      digest[11] := Nat8.fromIntWrap(Nat32.toNat(s2 & 0xff));
+      digest[12] := Nat8.fromIntWrap(Nat32.toNat((s3 >> 24) & 0xff));
+      digest[13] := Nat8.fromIntWrap(Nat32.toNat((s3 >> 16) & 0xff));
+      digest[14] := Nat8.fromIntWrap(Nat32.toNat((s3 >> 8) & 0xff));
+      digest[15] := Nat8.fromIntWrap(Nat32.toNat(s3 & 0xff));
+      digest[16] := Nat8.fromIntWrap(Nat32.toNat((s4 >> 24) & 0xff));
+      digest[17] := Nat8.fromIntWrap(Nat32.toNat((s4 >> 16) & 0xff));
+      digest[18] := Nat8.fromIntWrap(Nat32.toNat((s4 >> 8) & 0xff));
+      digest[19] := Nat8.fromIntWrap(Nat32.toNat(s4 & 0xff));
+      digest[20] := Nat8.fromIntWrap(Nat32.toNat((s5 >> 24) & 0xff));
+      digest[21] := Nat8.fromIntWrap(Nat32.toNat((s5 >> 16) & 0xff));
+      digest[22] := Nat8.fromIntWrap(Nat32.toNat((s5 >> 8) & 0xff));
+      digest[23] := Nat8.fromIntWrap(Nat32.toNat(s5 & 0xff));
+      digest[24] := Nat8.fromIntWrap(Nat32.toNat((s6 >> 24) & 0xff));
+      digest[25] := Nat8.fromIntWrap(Nat32.toNat((s6 >> 16) & 0xff));
+      digest[26] := Nat8.fromIntWrap(Nat32.toNat((s6 >> 8) & 0xff));
+      digest[27] := Nat8.fromIntWrap(Nat32.toNat(s6 & 0xff));
+
+      return Blob.fromArrayMut(digest)
+    }
+  }; // class SHA224
+
+  func nat32ToByteArray(n : Nat32) : [Nat8] {
+    func byte(n : Nat32) : Nat8 {
+      Nat8.fromNat(Nat32.toNat(n & 0xff))
+    };
+    [byte(n >> 24), byte(n >> 16), byte(n >> 8), byte(n)]
   }
 }
diff --git a/test/Principal.test.mo b/test/Principal.test.mo
new file mode 100644
index 00000000..b88ee6e9
--- /dev/null
+++ b/test/Principal.test.mo
@@ -0,0 +1,53 @@
+import Principal "mo:base/Principal";
+import Text "mo:base/Text";
+import Blob "mo:base/Blob";
+import Suite "mo:matchers/Suite";
+import T "mo:matchers/Testable";
+import M "mo:matchers/Matchers";
+
+let BlobTestable : T.Testable<Blob> = object {
+  public func display(blob : Blob) : Text {
+    debug_show blob
+  };
+  public func equals(blob1 : Blob, blob2 : Blob) : Bool {
+    blob1 == blob2
+  }
+};
+
+let principal1 = Principal.fromText("un4fu-tqaaa-aaaab-qadjq-cai");
+let defaultAccount1 : Blob = "\57\4E\66\E1\B5\DD\EF\EA\78\73\6B\E4\6C\4F\61\21\31\98\88\90\08\2E\E8\0F\97\F6\B6\DB\ED\72\84\1E";
+let subAccount1 : Blob = "\4A\8D\3F\2B\6E\01\C8\7D\9E\03\B4\56\7C\F8\9A\01\D2\34\56\78\9A\BC\DE\F0\12\34\56\78\9A\BC\DE\F0";
+let accountWithSubAccount1 : Blob = "\8C\5C\20\C6\15\3F\7F\51\E2\0D\0F\0F\B5\08\51\5B\47\65\63\A9\62\B4\A9\91\5F\4F\02\70\8A\ED\4F\82";
+
+let principal2 = Principal.fromText("ylia2-w3sds-lgwx6-swrzr-xctdp-2rukx-uothy-yh5te-i5rt6-fqg62-iae");
+let defaultAccount2 : Blob = "\CA\04\B1\21\82\A1\6F\55\59\D0\63\BB\F4\46\CB\A2\F8\49\51\FE\1D\13\7C\E7\D7\45\85\1B\B2\96\6E\08";
+let subAccount2 : Blob = "\4F\8B\12\A5\C3\E6\07\D9\1F\A2\B0\C4\67\E8\90\23\4A\B6\5D\C8\91\0E\F2\47\8A\CD\56\B3\9E\01\2F\84";
+let accountWithSubAccount2 : Blob = "\D4\40\35\AF\5D\1D\6A\37\5F\F6\26\E6\9E\17\FA\44\B3\9C\31\FE\17\D3\3A\54\FF\4C\E4\C6\F0\FA\DA\EC";
+
+let suite = Suite.suite(
+  "Principal",
+  [
+    Suite.test(
+      "toLedgerAccount, default sub-account 1",
+      Principal.toLedgerAccount(principal1, null),
+      M.equals({ BlobTestable and { item = defaultAccount1 } })
+    ),
+    Suite.test(
+      "toLedgerAccount, with sub-account 1",
+      Principal.toLedgerAccount(principal1, ?subAccount1),
+      M.equals({ BlobTestable and { item = accountWithSubAccount1 } })
+    ),
+    Suite.test(
+      "toAccount, default sub-account 2",
+      Principal.toLedgerAccount(principal2, null),
+      M.equals({ BlobTestable and { item = defaultAccount2 } })
+    ),
+    Suite.test(
+      "toLedgerAccount, with sub-account 2",
+      Principal.toLedgerAccount(principal2, ?subAccount2),
+      M.equals({ BlobTestable and { item = accountWithSubAccount2 } })
+    )
+  ]
+);
+
+Suite.run(suite)