diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..66175ed
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+.vessel/
diff --git a/README.md b/README.md
index b1eb3c5..09d3cfe 100644
--- a/README.md
+++ b/README.md
@@ -1 +1,19 @@
 # Crypto Package for Motoko
+
+## Packages
+
+| Package Name | Description | Path |
+|--------------|-------------|------|
+| SHA | SHA224 and SHA256 hash algorithms as defined in FIPS 180-4 | crypto/SHA |
+
+## Usage
+
+```motoko
+SHA256.sum(Blob.toArray(Text.encodeUtf8("hello world\n"))
+// "A948904F2F0F479B8F8197694B30184B0D2ED1C1CD2A1EC0FB85D299A192A447"
+
+let h = SHA256.New();
+h.write(Blob.toArray(Text.encodeUtf8("hello world\n")));
+h.sum([]);
+// "A948904F2F0F479B8F8197694B30184B0D2ED1C1CD2A1EC0FB85D299A192A447"
+```
diff --git a/package-set.dhall b/package-set.dhall
new file mode 100644
index 0000000..0827038
--- /dev/null
+++ b/package-set.dhall
@@ -0,0 +1,2 @@
+let upstream = https://github.com/aviate-labs/package-set/releases/download/v0.1.3/package-set.dhall sha256:ca68dad1e4a68319d44c587f505176963615d533b8ac98bdb534f37d1d6a5b47
+in  upstream
diff --git a/src/Hash.mo b/src/Hash.mo
new file mode 100644
index 0000000..c2a0e82
--- /dev/null
+++ b/src/Hash.mo
@@ -0,0 +1,17 @@
+module Hash {
+    public type Hash = {
+        // Returns the block size of the hash.
+        blockSize() : Nat;
+        // Returns the checksum data.
+        checkSum() : [Nat8];
+        // Resets the hash to its initial state.
+        reset() : ();
+        // Returns the number of bytes that sum will return.
+        size() : Nat;
+        // Adds the current hash to the resulting slice.
+        // The underlying hash is not modified.
+        sum(bs : [Nat8]) : [Nat8];
+        // Adds data to the running hash.
+        write(bs : [Nat8]) : ();
+    };
+};
diff --git a/src/SHA/SHA2.mo b/src/SHA/SHA2.mo
new file mode 100644
index 0000000..e20aaa5
--- /dev/null
+++ b/src/SHA/SHA2.mo
@@ -0,0 +1,138 @@
+import Array "mo:base/Array";
+import Binary "mo:encoding/Binary";
+import Iter "mo:base/Iter";
+import Nat32 "mo:base/Nat32";
+import Nat64 "mo:base/Nat64";
+
+import Hash "../Hash";
+import Util "../Utilities";
+
+/// For internal use only.
+module {
+    // First thirty-two bits of the fractional parts of the cube roots of the 
+    // first sixty-four prime numbers.
+    private let K : [Nat32] = [
+        0x428a2f98, 0x71374491, 0xb5c0fbcf, 0xe9b5dba5, 0x3956c25b, 0x59f111f1,
+        0x923f82a4, 0xab1c5ed5, 0xd807aa98, 0x12835b01, 0x243185be, 0x550c7dc3,
+        0x72be5d74, 0x80deb1fe, 0x9bdc06a7, 0xc19bf174, 0xe49b69c1, 0xefbe4786,
+        0x0fc19dc6, 0x240ca1cc, 0x2de92c6f, 0x4a7484aa, 0x5cb0a9dc, 0x76f988da,
+        0x983e5152, 0xa831c66d, 0xb00327c8, 0xbf597fc7, 0xc6e00bf3, 0xd5a79147,
+        0x06ca6351, 0x14292967, 0x27b70a85, 0x2e1b2138, 0x4d2c6dfc, 0x53380d13,
+        0x650a7354, 0x766a0abb, 0x81c2c92e, 0x92722c85, 0xa2bfe8a1, 0xa81a664b,
+        0xc24b8b70, 0xc76c51a3, 0xd192e819, 0xd6990624, 0xf40e3585, 0x106aa070,
+        0x19a4c116, 0x1e376c08, 0x2748774c, 0x34b0bcb5, 0x391c0cb3, 0x4ed8aa4a,
+        0x5b9cca4f, 0x682e6ff3, 0x748f82ee, 0x78a5636f, 0x84c87814, 0x8cc70208,
+        0x90befffa, 0xa4506ceb, 0xbef9a3f7, 0xc67178f2,
+    ];
+
+    // Initial hash value, H(0).
+    private let H256 : [Nat32] = [
+        0x6a09e667, 0xbb67ae85, 0x3c6ef372, 0xa54ff53a, 0x510e527f, 0x9b05688c,
+        0x1f83d9ab, 0x5be0cd19,
+    ];
+
+    public class SHA2(
+        initialState : [Nat32],
+        hashSize     : Nat,
+    ) : Hash.Hash = {
+        private var h   : [var Nat32] = Array.thaw<Nat32>(initialState);
+        private var x   : [var Nat8]  = Array.init<Nat8>(64, 0);
+        private var nx  : Nat         = 0;
+        private var len : Nat64       = 0;
+
+        public func blockSize() : Nat { 64; };
+
+        public func reset() : () {
+            h   := Array.thaw<Nat32>(initialState);
+            x   := Array.init<Nat8>(64, 0);
+            nx  := 0;
+            len := 0;
+        };
+
+        public func size() : Nat { hashSize; };
+
+        public func sum(bs : [Nat8]) : [Nat8] {
+            Array.append(bs, checkSum());
+        };
+
+        public func checkSum() : [Nat8] {
+            let n = len;
+            var tmp = Array.init<Nat8>(64, 0);
+            tmp[0] := 0x80;
+            if (Nat64.toNat(len) % 64 < 56) {
+                write(Util.takeN<Nat8>(
+                    56 - Nat64.toNat(len) % 64,
+                    Array.freeze(tmp),
+                ));
+            } else {
+                write(Util.takeN<Nat8>(
+                    64 + 56 - Nat64.toNat(len) % 64, 
+                    Array.freeze(tmp),
+                ));
+            };
+            write(Binary.BigEndian.fromNat64(n << 3));
+            var digest : [Nat8] = [];
+            label l for (i in h.keys()) {
+                if (i == 7 and hashSize == 28) { break l; };
+                digest := Array.append(digest, Binary.BigEndian.fromNat32(h[i]));
+            };
+            digest;
+        };
+
+        public func write(bs : [Nat8]) : () {
+            var p = bs;
+            len +%= Nat64.fromNat(bs.size());
+            if (0 < nx) {
+                let n = Util.copy<Nat8>(nx, x, p);
+                nx += n;
+                if (nx == 64) {
+                    block(Array.freeze(x));
+                    nx := 0;
+                };
+                p := Util.removeN(n, p);
+            };
+            if (64 <= p.size()) {
+                let n = Nat64.toNat(Nat64.fromNat(p.size()) & (^63));
+                block(Util.takeN(n, p));
+                p := Util.removeN(n, p);
+            };
+            if (0 < p.size()) {
+                nx := Util.copy<Nat8>(0, x, p);
+            };
+        };
+
+        private func block(bs : [Nat8]) {
+            var p = bs;
+            var w : [var Nat32] = Array.init<Nat32>(64, 0);
+            var h0 = h[0]; var h1 = h[1]; var h2 = h[2]; var h3 = h[3];
+            var h4 = h[4]; var h5 = h[5]; var h6 = h[6]; var h7 = h[7];
+            while (64 <= p.size()) {
+                for (i in Iter.range(0, 15)) {
+                    let j = i * 4;
+                    w[i] := Util.nat8to32(p[j]) << 24  | Util.nat8to32(p[j+1]) << 16
+                          | Util.nat8to32(p[j+2]) << 8 | Util.nat8to32(p[j+3]);
+                };
+                for (i in Iter.range(16, 63)) {
+                    let v1 = w[i-2];
+                    let t1 = (Nat32.bitrotRight(v1, 17) ^ Nat32.bitrotRight(v1, 19)) ^ (v1 >> 10);
+                    let v2 = w[i-15];
+                    let t2 = (Nat32.bitrotRight(v2, 7) ^ Nat32.bitrotRight(v2, 18)) ^ (v2 >> 3);
+                    w[i] := t1 +% w[i-7] +% t2 +% w[i - 16];
+                };
+                var a = h0; var b = h1; var c = h2; var d = h3;
+                var e = h4; var f = h5; var g = h6; var h = h7;
+                for (i in Iter.range(0, 63)) {
+                    let t1 = h +% (Nat32.bitrotRight(e, 6) ^ Nat32.bitrotRight(e, 11) ^ Nat32.bitrotRight(e, 25)) +% ((e & f) ^ (^e & g)) +% K[i] +% w[i];
+                    let t2 = (Nat32.bitrotRight(a, 2) ^ Nat32.bitrotRight(a, 13) ^ Nat32.bitrotRight(a, 22)) +% ((a & b) ^ (a & c) ^ (b & c));
+                    h := g; g := f; f := e; e := d +% t1;
+                    d := c; c := b; b := a; a := t1 +% t2;
+                };
+                h0 +%= a; h1 +%= b; h2 +%= c; h3 +%= d;
+                h4 +%= e; h5 +%= f; h6 +%= g; h7 +%= h;
+                p := Util.removeN(64, p);
+            };
+            h[0] := h0; h[1] := h1; h[2] := h2; h[3] := h3;
+            h[4] := h4; h[5] := h5; h[6] := h6; h[7] := h7;
+        };
+    };
+};
diff --git a/src/SHA/SHA224.mo b/src/SHA/SHA224.mo
new file mode 100644
index 0000000..da94dd9
--- /dev/null
+++ b/src/SHA/SHA224.mo
@@ -0,0 +1,20 @@
+import SHA2 "SHA2";
+
+import Hash "../Hash";
+
+module SHA224 {
+    // Initial hash value, H(0).
+    private let H224 : [Nat32] = [
+        0xc1059ed8, 0x367cd507, 0x3070dd17, 0xf70e5939, 0xffc00b31, 0x68581511,
+        0x64f98fa7, 0xbefa4fa4,
+    ];
+
+    /// Returns the SHA224 checkum of the data.
+    public func sum(bs : [Nat8]) : [Nat8] {
+        let h = New();
+        h.write(bs);
+        h.checkSum()
+    };
+
+    public func New() : Hash.Hash { SHA2.SHA2(H224, 28); };
+};
diff --git a/src/SHA/SHA256.mo b/src/SHA/SHA256.mo
new file mode 100644
index 0000000..faff330
--- /dev/null
+++ b/src/SHA/SHA256.mo
@@ -0,0 +1,20 @@
+import SHA2 "SHA2";
+
+import Hash "../Hash";
+
+module SHA224 {
+    // Initial hash value, H(0).
+    private let H256 : [Nat32] = [
+        0x6a09e667, 0xbb67ae85, 0x3c6ef372, 0xa54ff53a, 0x510e527f, 0x9b05688c,
+        0x1f83d9ab, 0x5be0cd19,
+    ];
+
+    /// Returns the SHA256 checksum of the data.
+    public func sum(bs : [Nat8]) : [Nat8] {
+        let h = New();
+        h.write(bs);
+        h.checkSum();
+    };
+
+    public func New() : Hash.Hash { SHA2.SHA2(H256, 32); };
+};
diff --git a/src/Utilities.mo b/src/Utilities.mo
new file mode 100644
index 0000000..eb77c59
--- /dev/null
+++ b/src/Utilities.mo
@@ -0,0 +1,46 @@
+import Array "mo:base/Array";
+import Nat8 "mo:base/Nat8";
+import Nat32 "mo:base/Nat32";
+
+module Utilities {
+    public func copy<T>(
+        n   : Nat, // Position to start writing.
+        dst : [var T], 
+        src : [T],
+    ) : Nat {
+        let l = dst.size();
+        for (i in src.keys()) {
+            if (l <= i) return l;
+            dst[n + i] := src[i];
+        };
+        src.size();
+    };
+
+    public func removeN<T>(
+        n  : Nat, // Number to remove.
+        xs : [T],
+    ) : [T] {
+        Array.tabulate<T>(
+            xs.size() - n,
+            func (i : Nat) : T {
+                xs[i + n];
+            },
+        );
+    };
+
+    public func takeN<T>(
+        n  : Nat, // Number to take.
+        xs : [T],
+    ) : [T] {
+        Array.tabulate<T>(
+            n,
+            func (i : Nat) : T {
+                xs[i];
+            },
+        );
+    };
+
+    public func nat8to32(n : Nat8) : Nat32 {
+        Nat32.fromNat(Nat8.toNat(n));
+    };
+};
diff --git a/test/SHA224.mo b/test/SHA224.mo
new file mode 100644
index 0000000..13342d0
--- /dev/null
+++ b/test/SHA224.mo
@@ -0,0 +1,24 @@
+import Blob "mo:base/Blob";
+import Hex "mo:encoding/Hex";
+import Text "mo:base/Text";
+
+import SHA224 "../src/SHA/SHA224";
+
+let sum224 = SHA224.sum(Blob.toArray(Text.encodeUtf8("hello world\n")));
+assert(Hex.encode(sum224) == "95041DD60AB08C0BF5636D50BE85FE9790300F39EB84602858A9B430");
+
+for (v in [
+    ("", "D14A028C2A3A2BC9476102BB288234C415A2B01F828EA62AC5B3E42F"),
+    ("a", "ABD37534C7D9A2EFB9465DE931CD7055FFDB8879563AE98078D6D6D5"),
+    ("ab", "DB3CDA86D4429A1D39C148989566B38F7BDA0156296BD364BA2F878B"),
+    ("abc", "23097D223405D8228642A477BDA255B32AADBCE4BDA0B3F7E36C9DA7"),
+    ("abcd", "A76654D8E3550E9A2D67A0EEB6C67B220E5885EDDD3FDE135806E601"),
+    ("abcde", "BDD03D560993E675516BA5A50638B6531AC2AC3D5847C61916CFCED6"),
+    ("abcdef", "7043631CB415556A275A4EBECB802C74EE9F6153908E1792A90B6A98"),
+    ("abcdefg", "D1884E711701AD81ABE0C77A3B0EA12E19BA9AF64077286C72FC602D"),
+    ("abcdefgh", "17EB7D40F0356F8598E89EAFAD5F6C759B1F822975D9C9B737C8A517"),
+    ("abcdefghi", "AEB35915346C584DB820D2DE7AF3929FFAFEF9222A9BCB26516C7334"),
+    ("abcdefghij", "D35E1E5AF29DDB0D7E154357DF4AD9842AFEE527C689EE547F753188"),
+].vals()) {
+    assert(Hex.encode(SHA224.sum(Blob.toArray(Text.encodeUtf8(v.0)))) == v.1);
+};
diff --git a/test/SHA256.mo b/test/SHA256.mo
new file mode 100644
index 0000000..a22e5f2
--- /dev/null
+++ b/test/SHA256.mo
@@ -0,0 +1,38 @@
+import Blob "mo:base/Blob";
+import Hex "mo:encoding/Hex";
+import Text "mo:base/Text";
+
+import Debug "mo:base/Debug";
+
+import SHA256 "../src/SHA/SHA256";
+
+let sum256 = SHA256.sum(Blob.toArray(Text.encodeUtf8("hello world\n")));
+assert(Hex.encode(sum256) == "A948904F2F0F479B8F8197694B30184B0D2ED1C1CD2A1EC0FB85D299A192A447");
+
+let h = SHA256.New();
+h.write(Blob.toArray(Text.encodeUtf8("hello world\n")));
+assert(Hex.encode(sum256) == Hex.encode(h.sum([])));
+
+for (v in [
+    ("", "E3B0C44298FC1C149AFBF4C8996FB92427AE41E4649B934CA495991B7852B855"),
+    ("a", "CA978112CA1BBDCAFAC231B39A23DC4DA786EFF8147C4E72B9807785AFEE48BB"),
+    ("ab", "FB8E20FC2E4C3F248C60C39BD652F3C1347298BB977B8B4D5903B85055620603"),
+    ("abc", "BA7816BF8F01CFEA414140DE5DAE2223B00361A396177A9CB410FF61F20015AD"),
+    ("abcd", "88D4266FD4E6338D13B845FCF289579D209C897823B9217DA3E161936F031589"),
+    ("abcde", "36BBE50ED96841D10443BCB670D6554F0A34B761BE67EC9C4A8AD2C0C44CA42C"),
+    ("abcdef", "BEF57EC7F53A6D40BEB640A780A639C83BC29AC8A9816F1FC6C5C6DCD93C4721"),
+    ("abcdefg", "7D1A54127B222502F5B79B5FB0803061152A44F92B37E23C6527BAF665D4DA9A"),
+    ("abcdefgh", "9C56CC51B374C3BA189210D5B6D4BF57790D351C96C47C02190ECF1E430635AB"),
+    ("abcdefghi", "19CC02F26DF43CC571BC9ED7B0C4D29224A3EC229529221725EF76D021C8326F"),
+    ("abcdefghij", "72399361DA6A7754FEC986DCA5B7CBAF1C810A28DED4ABAF56B2106D06CB78B0"),
+].vals()) {
+    assert(Hex.encode(SHA256.sum256(Blob.toArray(Text.encodeUtf8(v.0)))) == v.1);
+};
+
+do {
+    let h = SHA256.New();
+    h.write(Blob.toArray(Text.encodeUtf8("hello")));
+    h.write(Blob.toArray(Text.encodeUtf8(" ")));
+    h.write(Blob.toArray(Text.encodeUtf8("world")));
+    assert(Hex.encode(h.sum([])) == "B94D27B9934D3E08A52E52D7DA7DABFAC484EFE37A5380EE9088F7ACE2EFCDE9");
+};
diff --git a/test/Utilities.mo b/test/Utilities.mo
new file mode 100644
index 0000000..c56b0a7
--- /dev/null
+++ b/test/Utilities.mo
@@ -0,0 +1,18 @@
+import Array "mo:base/Array";
+import Iter "mo:base/Iter";
+
+import Util "../src/Utilities";
+
+let fifty   = Iter.toArray(Iter.range(0, 49));
+let hundred = Iter.toArray(Iter.range(0, 99));
+
+// Remove the first 50.
+assert(Util.removeN(50, hundred) == Iter.toArray(Iter.range(50, 99)));
+
+// Take the first 50.
+assert(Util.takeN(50, hundred) == fifty);
+
+// Copy the first 50 starting at position 50.
+let copyTo = Array.thaw<Nat>(hundred);
+assert(Util.copy(50, copyTo, Util.takeN(50, hundred)) == 50);
+assert(Array.freeze(copyTo) == Array.append(fifty, fifty));
diff --git a/vessel.dhall b/vessel.dhall
new file mode 100644
index 0000000..3068d14
--- /dev/null
+++ b/vessel.dhall
@@ -0,0 +1,4 @@
+{
+  dependencies = [ "base", "encoding" ],
+  compiler = Some "0.6.10"
+}
\ No newline at end of file